Each magecraft ability has a different effect, although they all have the same trigger condition, whenever you cast or copy an instant or sorcery spell.

If an effect creates multiple copies of an instant or sorcery spell, magecraft abilities trigger once for each copy created by the effect.

Some effects instruct you to copy an instant or sorcery card in a zone other than the stack. These copies do not cause magecraft abilities to trigger. However, most effects that do this also allow you to cast the copy, and casting the copy will cause magecraft abilities to trigger.

If an effect creates a copy of an instant or sorcery spell, this will also cause the magecraft ability to trigger.

For example, if you control Archmage Emeritus and cast an instant or sorcery spell, Archmage Emeritus’s magecraft ability will trigger and you will draw a card.

To double the number of +1/+1 counters on a permanent, put a number of +1/+1 counters on it equal to the number it already has. Other cards that interact with putting counters on it will interact with this effect accordingly.