If you want to write your own songs, you don't need to read music, have a fancy recording setup, or even play an instrument (although those things are great). All you need is a recording device, like a cellphone, and your voice. So now what? Well, most songs have words and they have music. You can start by working on one at a time. To practice writing lyrics, why not change the words of an existing song? (Kids do this all the time.) That way you can get a sense for they way words fit into a melody. If you want to practice your melody writing, you can do the opposite, that is, setting a poem to music. Try reading the lyrics of a song you've never heard. Now imagine what the tune might sound like. The more you practice, the easier it gets.
Elizabeth Bruce - songwriting, voice & piano instructor