[Question] How do I make RMXP tilesets?

I wonder how I can implement a tileset I just found into RPGMXP, its always not compatible or too big or too little, how can I make it fit?
It has more parts like opening doors (these 4x4 doors) or trees, its not transparent. What do I have to do? Put in PS and stretch it ?

Thanks for answers :)

just use this tileset base: http://www.deviantart.com/art/RMXP-s-Tileset-Base-210166220
this is a good way to check whether you tileset does fit or not.

Thanks, do I have to cut now every single tile out of the tileset or how do I do that? It has 4000x4000 pixels, when I implement it on this base it gets small.

Can you maybe give me something like a step by step ? ^^* I am maybe to stupid for that