Go to your song library
Press the 'New song' button.
On the New Song screen, enter the basic details for the song. The only thing that you must provide is the song title. If possible, make sure that the key and capo position match the chords of the song - this isn't totally necessary, but will allow Chordle to accurately reflect the true key of your song if it gets transposed later on.
Enter the text and chords for the song, spacing the chords out so that they appear in the right place above the line they belong to. You can often find the chords for songs on other sites, such as Ultimate Guitar.
Optionally you can also add tags to your song. These are helpful for when you're searching for songs later on. By tagging songs with helpful keywords, e.g. the tempo of the song, 'slow'/'upbeat' or its theme, 'grace'/'family', you can find songs more quickly if you need something to fit a specific mood.
Finally, press the save button.