You can see stats in the upper right corner. Those white bars are all the info you’ll get, no numbers, unless you painstakingly test them. Stats levels range from 0 to 255.
Toggle their training by left-clicking their respectable stones in the lower-right corner, or toggle their visibility by right clicking that (or tapping + on the numpad).
Selecting a group of units, the one with the most overall stat points is selected as the leader.
The overall stat number is directly related to the xp value of a unit. This means flimsy Rhamphorhynchuses are worth a lot due to their high VP, and Spellcasters can generally be worth more thanks to the extra MP statistic.
A Tiger gives more xp than the hardier Musso, simply because of high VP.
HP
Hit Points (Health Power)
You lose them, you die. There are many ways to get them back though. Elven spells, eating snacks or meat, sleeping (you can eat food while sleeping!), and there even is a basic regeneration for critically wounded units.
Health bar appears over the unit and comes in many colors. It represents only HP.
Each color (except red ones) represents 40 hp.
70 points are required for Commoners to become a Muscle-Man.
Furthermore, each health point equals to 64 points of food that a unit can pick up and not feel the urge to deposit it in the bank immediately. So a Commoner (30 HP) can pick up 1919 food (64×30-1) and continue to hunt. 1920 food and he goes to the food storage. A 255 HP unit can carry 16319 no sweat.
OP
Offense Points (Offense Power)
Very important points. They make you win faster. They increase the damage dealt. That’s all. No attack speed, no range, only damage.
Also 70 are required for Commoners to become Warriors.
DP
Defense Points (Defense Power)
They reduce the damage taken.
They do not protect against spells, but do so against basic spellcaster attacks. DP also won’t block mushroom or weed damage, but helps against Dilophosaurus breath.
Shields provide no bonus against any of those types of attack though.
MP
Magic Points (Magic Power)
You need them to learn and cast spells. They regenerate slowly, but don’t require food.
You can speed it up by sleeping, snacking or finding a dedicated legendary item:
Wizard – Skull Stick
Warlock – Rock Crystal
Elf – Mystical Liquor
Ranger – Eye of the Dragon
Freshly trained spellcasters know only their first spell. To work around that bug and get more, make them learn only MP and go kill something. Even a commoner will do sometimes, a single MP+1 to reset the spell counter is enough. Simply hunting without MP priority may take a lot of time, because weaker stats raise first.
VP
Velocity / View Points (or Power)
They affect sight radius, range of ranged attacks, range of casting spells and move speed.
The attack range depends on weapons. A fresh commoner has the same pathetic minimum 3 tile range with a bow and a boomerang. A unit with max VP sports a 4 tile range difference between those two weapons. 10 for the bow, 6 for the boomerang.
Spellcasters’ basic attack range scales like the bow. So 10’s maximum for the basic attack, but individual spells can have higher or lower range.
Roughly the first 1/3 of VP bar gives two tiles of bonus spell casting range. The other 2/3 give just two more.
The Dilophosaurus doesn’t increase its range.
Movement speed similarly has thresholds of improvement, it is not linear. First is passed when a unit earns it’s 96th point of VP, an equivalent of getting a dark blue HP bar. There are four tiers of move speed in total, their tresholds are 96, 161 and 225 VP.
The speed of all projectiles is the same, and they can be evaded.
There exists a freshman bug. Fresh units move with lowest speed, 
regardless of VP. You have to „wake them up” by clicking an action, or even hovering over something attackable. The speed is then reset to one that is relevant to their VP. On the right I have „waken up” a lower tier Rhampho and it is faster than a higher tier one. When „awaken”, the higher tier would be even faster. Resurrected units also have some problems with remembering to move with their max speed.
Maybe „waking up” is not the best term, because ordering a unit to go to sleep effectively „wakes them up” 😛
Setting them up
Basic stat learn pattern is set like this:
VP may be less useful for melee units. HP and DP, while always adding to survivability, is not the best choice for designated archers.
Leveling a Commoner to a Muscle-Man with the default stats set takes a long time, as DP and VP get priority somehow. To acquire a Warrior, HP must not get to 70 points first, and it always increases before OP in the default pattern.
Spellcasters have these set on default instead:
VP is very useful for them though, but it’s your choice. I’d level MP first to unlock some spells. They appear on 30/50/70/90/110 MP thresholds, depending on the caster. That’s a lot of training, but higher level units already have these stats, they just need a single point to kind of „recall” the better spells.
Elves and Rangers desperately need OP to be useful in combat. HP and DP help Elves conserve MP they use for healing. DP more so in the early missions, where only the simple healing is available. Their spells are triggered by a significant relative loss of HP, and if the health bar is fat, the less MP is wasted. VP helps them attack en masse and heal at longer range.
Rangers level 1 have a good VP score, Rangers level 2 have a great VP score. But the level 2 ones are just 6 points short of a sight range extension and a leap in movement speed. Their spells make the VP kind of redundant though. They need 40 more MP to learn Resuscitation, but it’s the most useful spell in the game, so it’s worth it. VP doesn’t extend the range of their spells at all (just the last spell – a tiny bit), but extra attack range paired with teleportation helps with outmaneuvering stronger hostiles.
Wizards and Warlocks are less OP dependent, but it’s always useful. Warlocks have decent VP, Wizards have decent HP. Wizards can freeze a unit and run, Warlocks are rather… expendable by nature.
Early stat levels are easier to obtain than the late ones. An enemy that gives a lot experience for a weak character can give none to a hero.
Stats level up together. Only the lowest selected stats will level up, until all are at the same level. When leveling the chosen stats is impossible, the other stats are trained.
Difficulty
Units’ stats are dependent on the difficulty setting, but for some reason, only starting units are changed – the ones present on the map from the beginning. Trained units and respawned neutral units have normal difficulty stats.
EASY:
Your starting units enjoy +15 to all stats (even MP)
Enemy and neutral starting units have a -10 to HP, OP and DP
NORMAL:
Stats are the same for starting and subsequent units.
They equal the ones in the tables on this site.
HARD:
All your units have normal difficulty stats.
Enemy and neutral starting units get a +15 bonus.