Create a written guide that enables others to perform the song. Write out lyrics in proper stanza form with the chord changes written above the words. If you are able to write music, create sheet music layered first with piano accompaniment then a treble clef line of melody.
Copyright your music by registering the works with the U.S. Copyright Office. This will ensure your rights to the songs and provide proof of your ownership of the copyright in the event someone else tries to claim the music as their own.
Find a music publisher or self-publish your music. Music publishers are able to shop your music to a wide variety of potential buyers, including advertising agencies, managers for musical acts and musical directors for movies. Contact music publishers to inquire about possible publishing deals for your music that ensure you will be paid royalties for your creation. One good place to start is the Music Publishers Association at mpa.org. If you choose to self-publish, you are then responsible for marketing and promoting your music to potential buyers.