Just start writing. Maybe it’s prose at first, maybe it poetry. Find some of the phrases that resonate and feel true and use them as kind of landmarks. Be specific in detail rather than broad. Generalities won’t connect as much and feel like ad copy whereas a specific personal detail can be felt by an audience, even if it isn’t true to their life. If you have a rhythm in mind you can start mapping your words to that. They don’t need to match perfectly, but think about phrases or lines fitting with or dancing around the beat, whatever suits the music and the content. Then, try it out. If it doesn’t work don’t throw the whole thing out but rework it keeping parts that you like. If you are just starting writing songs, there is nothing wrong with borrowing some style from artists you admire (without plagiarizing). Play it for some friends and be open to feedback. Criticism of your creative work is not criticism of you, it helps you get closer to making something great.