Putting in a custom entity?

Hi, im making a game mode and am wanting to put Helicopters on a map that i got off gmod.org and am just unsure on how to do that.

spawn any entity (e.g. info_player_start) and change the name to whatever the entity name is (e.g. ent_helicopter)

It worked,Thanks for your help!

If you have an entity which has variables, you can create an entity for hammer with a custom .fgd.