If they are GUI spells, you have to File -> Preferences -> Automatically create unknown variables while pasting trigger data. Then, copy the folder of the spell you want, go to your map and Edit -> Paste it. You also have to go to the Object Editor and check everything used by the spell: Units/Abilities/Buffs.
If it is a Jass spell, you will need to copy everything out of the Object Editor that is custom-made and you will create a new trigger in your map. Then, while your new trigger is on, go to Edit -> Convert to Custom text. You will receive a notification, press Ok. Select everything from the recently created text and delete it. Go back to the Jass spell in the other map, select the code from the spell, right click it and Copy. Return to your map and in the blank sheet of code you deleted previously, right click and Paste.
There are most likely instructions on how to implement your spell on almost every spell, especially Jass made ones.