Tactic skills?

They buff allies within two spaces of the user, granted those allies' movement types do not make up more than half of a regular-sized team (2 units). So if my team has 3 armors and 1 flier, only the flier will get the buff because there are 2 or less fliers on the team. If it has 2 armors and 2 fliers, every unit can get the buff.

The description confuses everyone :/
Don't worry. This stuff confused me the first time as well.
So basically you have to have more than two of a unit type for it to work. Say if you have two infantry units and two horse units, or one flying and armor and two infantry, then it will work. But if you have, say, three infantry units and a horse, then it won't.
Tactics work best with mixed teams so if you have something of the examples up there, Tactics work wonders.

You can't have more than two of the same movement type, otherwise it doesn't work. It encourages you to switch up your teams so as they're not a single "Emblem" type.