Buffs are timed advantages, e.g. more gather yield, faster smelting, more vitality or less radiation. In the "Buffs" tab you buy them for yourself, your team or your whole clan – paid with scrap from your inventory or with Radcoins.
Active buffs and their remaining time are shown at the edge of the screen (collapse with /buffhud); shortly before expiry you get a warning and can extend right away. The tab lets you compare buffs and see your history. You also get buffs from territory control, the login bonus (day 7), mushrooms during mushroom season and the server-wide blessing.
Commands
/buffs/buffhud