I think of a song as having lyrics, those being structured rhytmically to some extent, and with or without pitch changes.Songwriting. What does that word mean to you? and how do you do it?
I usually write a story or poem (often in rhyming verse) and decide on some approximate style/genre for it. For melodic parts, I decide on chord progressions that seem to fit with the mood of the lyrics (or counter it, if going for that intentionally), and then set the words/syllables to pitches that relate/contrast to the chords.
Deciding on pitches of syllables can be interesting challenge, especially when tailoring to a specific singer or aiming for "karaoke compatibility" (being easy to sing for anyone).
Also fun are the aspects of composing for different pitch ranges. What pitches to give to basses and baritones vs. to altos and sopranos; when can a melody be given to bass, etc.
And then there's the sound color/timbre to experiment with.
Nominally non-pitched lyrics are interesting to work with as well. Whispering, speechlike, rap, screamlike growl etc. Sometimes, when message of the lyrics is most important, trying to make the lines melodic/pitched can actually take away from the expression. At other times, making the lyrics clearly pitched is most effective. Both can happen in same song.
As always, learning from existing examples via analysis is fascinating.