Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities (such as equip) are activated abilities and will have colons in their reminder text.

If the activated ability's cost contains a choice, such as a creature to sacrifice or a number of counters to remove, the copy uses that same information. You can't pay the cost again, even if you want to.

If the ability is modal (that is, if it says, "Choose one —" or similar), the mode is copied and can't be changed.

The source of the copy is the same as the source of the original ability.

The copy made by Ertha Jo's triggered ability is created on the stack, so it's not "activated."

The copy will have the same targets as the ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. The new targets must be legal.

If an ability is linked to a second ability, copies of that ability are also linked to that second ability. If the second ability refers to "the exiled card," it refers to all cards exiled by the ability and the copy. For example, if one of Helvault's activated abilities is copied and two cards are exiled, they both return when Helvault is put into a graveyard from the battlefield.

If the ability divides damage or distributes counters among a number of targets, the division and number of targets can't be changed. If you choose new targets, you must choose the same number of targets.

Any choices made when the ability resolves won't have been made yet when it's copied. Any such choices will be made separately when the copy resolves.