You need to be registered and logged in to the Forums to post a song or playlist.
Upload song from the song view by tapping the Share button on the top right, then tap Share Chord Chart.

Tap on Forums. It will automatically copy the song to your clipboard and open the Forums.

Tap on Log in and enter your username and password.

Tap into the relevant forum area, then tap on New Thread to create a new one or reply to an existing one.

Add a title, then tap and hold in the post's Message window and paste the song.
After that just tap on Submit to upload the song.

A playlist can be shared or posted to the Forums as well with the above steps.