How do you extract files?

How can I extract abilities.slk or whatever i need to make custom spells from war3.mpq?

You can use one of these tools:
- MPQView (the fastest one, but make sure that you use the appropriate listfiles)
- WinMPQ (the easiest to use, but the slowest of these)
- TechMPQ (quite fast, but I don't recommend it as it's interface sucks)