How do I add levels and other stuff for my playerworld?

It's simple, making sure you have downloaded the latest Gserver, go into the 'world' folder, inside this folder you can place all of your levels/webgifs/heads/etc in this folder, to make it neater you can add other folders so it's not so messy. Just make sure it's all still in the 'world' folder. Also, make sure you have set a default and working onlinestartlocal.nw level in your levels.