I'm a technical guy, not a musician, so feel free to ignore me!
Where are you starting from? Do you play an instrument? Are you a singer? Are you a poet? Do you read music?
As you probably know, sometimes it's a partnership with one person writing the lyrics and the other person writing the music. Or, sometimes with the whole band pitching-in ideas to complete the song.
I'm not sure if you'll find a good tutorial... If you can find a community college class on songwriting, that would be great... A structured class helps to guide your learning, forces you to "do the work", and to evaluate your progress (and to be evaluated). And, you get an instructor and fellow students to learn from.
I think the main thing is, "Just do it!" You've been listening to music all your life, so you should have a reasonably good "feel" for how a song is put together.
Serious songwriters, songwriters that make money from their craft, often write at least one song a day... "10 percent inspiration and 90 percent perspiration." Of course, all of those "1-day songs" are not going to be great, but hopefully some of them will be good, or will have potential to be developed into something good. Then, when you do get inspired, you'll have the skills & experience (and self-discipline) to turn that inspiration into something real.
If you want to get more advanced you can get a book on music theory (or again, take a class).
P.S.
There is also software to help you with songwriting. One example is
Master Writer, that's supposed to help you with lyrics. (Rhyming, synonyms, alliterations, etc.)
any great tutorial to learn to write music?
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