But thing #1 is that you need to expect and accept that you are going to write a LOT of bad songs before you start writing decent ones. I mean the evolution is something like:

bad
not as bad
so so
kinda sorta decent
decent
kinda sorta okay
okay
kinda sort good
good

And those are not one song intervals.

What I am saying in a lighthearted way is that the only way to learn how to play darts is to throw a lot of darts. And the only way to learn how to shoot free throws is to shoot a lot of free throws. And the only way to hit a bulls eye at the gun range is to throw a LOT of rounds downrange.

The only way to learn how to write songs is to just write those bad songs as you grow. Figure out what your story is, write the story out in lines that have a cadence, feeling where beats would be. That gives you some idea for cadence and tempo. Remember that your tempo can't be so fast that you can't get the words out between breaths. Once the cadence of the lyrics fits the cadence of the music (you will feel where natural pulses fit together) then you start thinking about the melody. You may go through 4-5 different melodies before you are comfortable with one.

Just as an example, let's pick The Beatles Love Me Do. Think of those lyrics.

Love, love me do
You know I love you
I'll always be true
So please......
Love me do

and then think of how those lyrics lay against the cadence of the music. That is a loose definition of prosody, how lyrics and music work together.
Now think of their song I've Just Seen A Face. That is a very wordy lyric, but when you lay it against the tempo of the song, they fit together. Think of it like when you slip your hand into a baseball glove and the fingers of your hand naturally find their way into the fingers of the glove. That's what you are after.

This is also where some basic music lessons would help you if you have never taken any. Learning about tempo, where the "1" is in every measure, what a measure is, how to read what the little dots are all about, especially the time value of the quarter note, the half note, the whole note, what a dot behind a note means, tied notes... You don't need to go DEEP into theory, but basics. Like maybe knowing why the different key signatures have sharps and flats. Someone mentioned a chord wheel. When you look at the wheel, moving to the right, each new key adds one sharp. C has none, G has 1, D has 2, etc. When you see the relativity of G being the 5th note of the C scale, and D being the 5th note of the G scale and so forth, it starts to make sense quickly. And going to the left of the wheel you add 1 flat at a time, and those flats happen on the 4th note of a scale. So C has no flats, the 4th note of the C scale is F, and F has one flat. The 4th note of the F scale is B flat, which has 2 flats, and so on. Do you NEED to know that stuff to let BIAB wrote your music and go play at Billy's Bar? Nope! But knowing how to use those tools helps your songwriting craftsmanship like knowing a hammer from a chisel helps a carpenter. It would honestly become clear to you quickly if you took a music fundamentals course at your local community college. Most young people these days learn songs. Nobody learns music.

I hope that made SOME kind of sense to you.