We used tool depends on where the field is you in, the Songwriter’s has tools too.
Audio recordings. If there’s a tune in mind, just sing it or play it on a tool of your choice, and use the recording feature on your computer or telephone to get it out of your mind and on paper… figuratively speaking.
Sheet Music. Alternatively, if you understand how to read and write sheet music, using a few blank pages handy is never a bad idea. You can refer back to what you wrote down. Having the ability to transcribe music to notes is a valuable skill.
Chord Names/Tablature. The piano and guitar are most likely the most frequently used instruments in traditional songwriting. Recall chord progressions by writing down the names of the chords or utilizing chord diagrams or guitar tablature.
Lyric Books. Many songwriters, myself included, have at least one laptop specializing in lyrics and lyrical ideas. This is particularly helpful when you’re on the move. The smallest thoughts are worth remembering as a couple of words or one line can grow to be a whole song. This may be accomplished digitally naturally. Many songwriters prefer physical laptops only because they like to have the ability to look back at where they left adjustments to an original set of lyrics.