BackupBackup is a triggered ability. “Backup N” means “When this creature enters, put N +1/+1 counters on target creature. If that’s another creature, it also gains the non-backup abilities of this creature printed below this one until end of turn.” Cards with backup have one or more abilities printed after the backup ability. (Some cards with backup also have abilities printed before the backup ability.)
If a permanent enters the battlefield as a copy of a permanent with a backup ability or a token is created that is a copy of that permanent, the order of abilities printed on it is maintained.
Only abilities printed on the object with backup are granted by its backup ability. Any abilities gained by a permanent, whether due to a copy effect, an effect that grants an ability to a permanent, or an effect that creates a token with certain abilities, are not granted by a backup ability.
The abilities that a backup ability grants are determined as the ability is put on the stack. They won’t change if the permanent with backup loses any abilities after the ability is put on the stack but before it resolves. (CR 702.165) 1 (When this creature enters, put a +1/+1
counterTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on target creature. If that's another creature, it gains the following ability until end of turn.)
LifelinkLifelink is a static ability.
Damage dealt by a source with lifelink causes that source’s controller, or its owner if it has no controller, to gain that much life (in addition to any other results that damage causes). See rule 120.3.
If an object is no longer in the zone it’s expected to be in as an effect causes it to deal damage, its last known information is used to determine whether it had lifelink.
The lifelink rules function no matter what zone an object with lifelink deals damage from.
If multiple sources with lifelink deal damage at the same time, they cause separate life gain events (see rules 119.9–10).
Multiple instances of lifelink on the same object are redundant. (CR 702.15)