Two different things that often get confused
Royalty splits (see the previous article) control where money goes. Track credits control metadata — who is officially listed as the writer, composer, lyricist, or author of a track, visible on the release itself. You can have accurate credits with no royalty split at all (if nobody but you needs a share of the money), and in principle you could have a royalty split with someone who isn't formally credited as a writer — though in practice these usually line up.
Why credits matter on their own
Correct writer/composer credits are what feeds publishing royalty collection (see "What is publishing administration?" in Publishing & Rights) and is part of the permanent metadata record for the track — this is what shows up in databases, is used for sync licensing inquiries, and is what collection societies reference when routing performance and mechanical royalties.
Adding credits to a track
When editing a track's details, add each contributor with their name and role — writer, composer, lyricist, or author are the standard roles recognized. You can add multiple people in the same role (e.g. two co-writers) or different roles for different people on the same track.
Where credits appear
Contributor credits show up in the track's metadata view in your dashboard and are included in the data delivered to stores and publishing administrators, depending on what each platform displays publicly.
If you're the only writer
If you wrote the entire track yourself and there's no co-writer or outside producer to credit, you don't need to add anything extra here — you're the default credited artist and songwriter unless you specify otherwise.