If I were you I'd learn a few more songs before trying to write your own, but here are some tips:
Start from a chord progression that you like the sound of. Experiment with it, play different chords in different sequences until you like the sound of the progression. You'll find that sticking to the related chords of the key is a good place to start*. Once you have the chord progression down, then start looking for a melody line. Do that with your voice. Using notes from the chords is a good place to start that process ... you can try singing real words that you have written, or use that strange non-language that most songwriters use which is based just on vowel sounds. Once you start getting a nice melodic idea going, then start to write some real words. The vibe of the chords/melody should help with the sentiment of the words. Obviously if your melody is bright and chirpy, you won't be singing about heartbreak; if it's dark and moody, you won't be writing about elusive butterflies.
It's a process which takes a bunch of loose ideas and eventually ties them all up into the 'song' ... at least that how it works for me.
If you're already a poet and you find writing words easy, then work the other way around. Seek out a basic melody line for the words, which should already have some sort of meter to them, then look for chords that will flesh out the melody line. Again, the related chords of the key are a good place to start.
Here the related chords for the keys of C, D and G. The majors are the 'primary' chords.
C ----> C - Dm - Em - F - G - Am
D ----> D - Em - F#m - G - A - Bm
G ----> G - Am - Bm - C - D - Em
Good luck!
