Welcome to the forum Frederick

Big question to answer, there are so many ways. A few ideas:
A musical idea* a chord sequence
* a riff
* an arpeggio
* a scale eg Pentatonic
* a fragment of another musician's music or sound that you make your own, we don't want lawsuits.
Your life * something you're passionate about
* an experience or event that means a lot to you
* love - lost, found, yearned for
* deep emotion
* something ridiculous or trivial
I've written three songs so far, so I have very little experience. My process usually starts with a phrase. It might be something I've heard or read or a thought that comes to me. I let it mush around in my head and some more words come to me, often just as I'm going to sleep, so I get up to write them down. Then I see the pictures that eventually become the verses. As the song begins to form a character I get the feeling and mood of the song. Next step for me to to listen to the music of others, that will often give me an idea of what I want. Then I figure out the melody. Last of all I figure out the chords.
I'd strongly recommend you keep a notebook where you write down any ideas or thoughts, even though you may not see where you're going with them. Once you start writing a song, you may find some gems in what you've written down.
I find I have creative, brain on fire times, and then dry spells, so make the most of it when you're on a roll. Let the words or notes pour out uncensored, you can cull and refine them later.
Most of all, make a start.