I hope that part of your filming is to get a variety of different angles and shots so your editing can be easier.
Start by picking your editing program. If you don't have one yet I recommend one of these.
You can use sound effects and music from creative commons places or you can make your own music.
If you want to look closer at the history of music in horror movies check out this clip.
A bonus here is a film that uses free special effect sounds and see if you can figure out how they did all their effects.
Closer look has several on horror movies so you should check them out.