If a creature with banding attacks, it can team up with any number of other attacking creatures with banding (and up to one nonbanding creature) and attack as a unit called a "band." The band can be blocked by any creature that could block a single creature in the band. Blocking any creature in a band blocks the entire band. If a creature with banding is blocked, the attacking player chooses how the blockers' damage is assigned.
A maximum of one nonbanding creature can join an attacking band no matter how many creatures with banding are in it.
Creatures in the same band must all attack the same player or planeswalker.
If a creature in combat has banding, its controller assigns damage for creatures blocking or blocked by it. That player can ignore the damage assignment order when making this assignment.
Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.