How to post a project in Planet Minecraft:

1. Hit the start button
2. Type "%appdata%" with quotes
3. You will see a folder called .minecraft. Double-click on it.
4. In there, you will see a "saves" Folder. Double click on that.
5. There, you will see a bunch of folders with your worlds' names
6. For now, you can minimize the folder. Now what we need to do is create a .zip Folder.
7. Right click on your desktop
8. Go to New > Compressed (zipped) Folder (If you have downloaded 7-zip or WinRAR, then click on that).
9. Open up the .zip folder
10. Bring back up the "saves" folder, and drag your desired world into that .zip folder
11. Upload it to Planet Minecraft

That's it!