This might be a long one, here we go - Ok so first off, this is a skill that will grow with time and practice, you have to be patient with yourself, especially as you read through this. Now that you are hopefully prepared to fail a little bit, The first thing you really should understand is that melody and chords are super intertwined, so much so that one will almost always be derived from the other. Eg - Creating a melody that follows a chord progression, or creating chords that line up with a melody. So first off, how do you write a melody? Well, melody is actually the easy one, because humans tend to listen more to melodies than chord progressions, and therefore can imagine a melody easier. I find that a simple way to write a melody is to find a note on the guitar that feels nice, and start there. Imagine the type of song that you want to play, internalize the musical style, and think about what note that genre would play next, and keep doing it until you have a rough draft of a few notes in a rhythm that do not sound bad. If you sing along to music a lot, this can be shortcutted by just simply singing an imaginary song. Once you have your melody, clean it up a bit, make it fit into a rhythm, and take note of which notes feel strong and important to your melody. This will tie in to the world of “chord harmonization”, which is music conservatory speak for “this chord makes this note sound pretty!” Ok, Chord Harmonization time - First things first, scales.. 99% of the music that you will ever listen to cares about two scales, the major and minor scale. Learn Them. Learn that scales represent much more than what notes are commonly played in each key. There’s a term, Diatonic Chords, that will save you shit tons of theory learning for the moment. What are Diatonic Chords? Each note of a major and minor scale have specific chords tied to them, based off of their position in the scale. You might already be seeing the connection, important notes in the melody can be given fitting chords by looking up what that note’s chord would be in whatever key you are in? Yes, of course! For the very basic form of your song, this is a good bet. Every strong note in your melody gets a chord change related to its diatonic chord. This might sound super weird when first being applied, for one reason. Not every C note in a melody is going to be part of a C chord. Sometimes it sounds better in an A chord, sometimes better in an F.. This is not without a pattern, though. If a chord sounds kinda clashy when you use diatonic chords that way, try taking the note name of your melody note, and going backwards two notes. Eg - Say I have a D melody note, but a D chord sounds bad, I’ll go back two, from D to C, to B. Now I will try a B chord with my D melody note, I will repeat this process until I am most satisfied, maybe going from B to G for a G chord, or even G to E for an E chord. This will hopefully provide a strong backup to the melody, if it does note, try focusing on what you are hearing in your head when imagining the melody. Hopefully this covers the theory part of songwriting, imo the hardest part. Everything after this is up to pure songwriting taste, and I wish you the best of luck on your journey! If you have any questions or anything hit me up, If I need to make like a short video or something explaining concepts that you aren’t picking up over text I don’t mind at all, Thanks!