Spent so much time making a piece of armor for the game (A helmet) and the tutorials I've been following are garbage. So its been a tough last 2 weeks of constant work...

Now I've finally finished editing properties for my (Probably buggy) file in nifskope and its ready to be put into the game but I have no idea how to do it

The .nif file is sitting in a folder.

I got Creation Kit and tried to add it as a new item but I get invalid directory. I can't put my .nif file into meshes because its a compressed BSA format. I can only extract stuff.

HELP, please.

Might help you out: http://www.youtube.com/playlist?list=PL3D12AF8D2C6A7875&feature=plcp

Hopefully you found a video that helped. If not, you can try http://www.creationkit.com/Customizing_Weapons_%26_Armor. Bethesda goes over the basics. You'd want to pick out a helm that has similar characteristics to yours (leather vs. metal, rarity, style, etc.), make a copy of it so you can name it whatever you like, then in your copy replace the default .nif with yours (hit the Edit button under the World Model).

Even though your .nif is in a BSA file it should still include a path since this is a Bethesda standard (it may even be required by the game but I'm not sure since I always follow their standard). If you really don't want to add a path you would simply specify the name of the .nif inside your BSA file. It will need to be a outside of the BSA file initially for the CK to find it.

In order for the BSA file to be used it will have to match the ESP file you create with your new armor. That is... if you saved your Armor definition in a file called "OwatchArmor.esp", the BSA will need to be called "OwatchArmor.bsa".