Most music is about chords and tunes.
There are seven basic chords called triads.
CEG DFA EGB FAC GBD ACE BDF (which isn't used much in basic composition)
Write a pattern of eight triads starting and ending on CEG and play it on a keyboard.
Choose a note in the first triad (CEG) and create a string of notes either:
by step up and down (steps),
or using the notes of the triad (jumps)
or a rhythm on the triad note, until you reach a note in the next triad.
Then repeat the process for the next triad and note until you have a complete tune!!
Composing can be so easy really...
Writing a "good" tune needs more structure but that is for another day...