Tactics: Every 20 points of tactics allows you to control one extra unit in battle. Each point of tactics adds 5hp to all your units. In addition, the player with the highest Tactics in any battle is automatically assigned as Battle Commander, which gets a 10% xp bonus at the end of that battle.
Clout: You need clout to gain access to more advanced units and unit upgrades (which means more space for stuff, better armor/hp/range/speed, and organic evolution). Every 2 clout gives you 1 Unit Quality point.
Unit UQ = Unit level + (Clout/2)
Unit Availability: Division level + (Clout/2) (defines what UQ level of units you can purchase)
Education: Education allows you to use higher tech equipment. For every 2 points of education you get 1 point of TL (Tech Level). This may seem like not much but it adds up. A player with a high education can get a lot better weapons and equipment - kill more efficiently. Basically if you want to kill a lot go tactics and education.
Tech Level = Unit Level + (Edu/2)
Mech Apt: MA allows your unit to carry more weight. Since every point of MA provides some effect of value, it is a great place to put all your remaining points after you have hit your goals in the other stats. For each MA point you get 1/120th of a units normal weight capacity; so units belonging to a hero with 120 MA can carry double what a normal unit gets as weight. MA helps new players equip everything they want, while it lets higher players put in the specifics they need.
Alien Tech Level: ATL determines power of organic units. Every 10 ATL, organic units get more health, armor, and damage.
ATL = Unit Level + (Edu + MA)/2
P.S. This info I took from relicwatchers.com with little modifications.