Custom Tilesets and Sounds

I'm sure this has been asked and I tried searching, but how do I import custom tilesets and custom sounds? when I made a tileset it worked and I played it but when OTHER people tried to play my level it was just the tileset I replaced not my own. 

Did you put it in your data folder? You need to make a sub-folder in the folder for your world called "Tilesets" and put the tilesets there. If you did that, it's probably a bug with the compression of your level.

Or even better, use the manager to ensure that you're doing it right.

I just got a tileset another user gave me and combined it with tileset 163 but when I put it in my level via manager the tileset background is white. Yet when I download an original copy of tileset 163 the background is transparent even though in paint they have the same background color.

it has to be transparent for the ks to read it transparent

try copy-transparent in ms paint

MS Paint can't work with the transparency that tilesets usually have, it replaces it with solid white and thus screws them up. Either you try replacing that white with magenta, or you use a different image editing program that can do transparency.

I would prefer paint.net over gimp.

Agreed. Paint.net has way more useful tools for pixeling that GIMP, and its also a lot easier to use.

There is no "best", beauty is in the eye of the beholder.

Paint.net and GIMP seem to be favorites around these parts (with a bias towards Paint.net)

There's also Graphics Gale, which is mostly useful for animations (custom objects are a breeze with this app), the free edition should supply you with all the tools you'll need.