C++ mods:
Upload it using any file uploader (dropbox for example), get the download link, copy it, make a new thread describing it, paste the download link and then post your thread.

Lua mods:
You can choose one of these options
1. Make a new thread describing your Lua mod, copy your code, paste it inside an opening code tag and a closing code tag (<code>YOUR CODE</code>) and then post your thread

2. Use pastebin, make a new pastebin, copy your code, paste it in that box, scroll down a little bit, change the settings if you want, save it, get the link, copy it, make a new thread describing your Lua mod and finally paste the link.

3. (the recommended way in my opinion) Upload your Lua file using any file uploader (dropbox for example), get the download link, copy it, make a new thread describing it, paste the download link and then post your thread.