Many official uploads carry a short block of credit lines, usually near the top of the description, and for a music video it is often followed by the lyrics or by a list of links. Each line names a role and then one or more names. The roles are different jobs, so the same person can appear on more than one line. Reading the block is largely a matter of taking it one line at a time instead of treating it as a single list of helpers.
Composed by, which some uploads write as Music by, points to who made the music, meaning the melody and the harmonic structure of the song as written. Lyrics by, sometimes written as Words by, points to who wrote the words. Written by is a broader phrase that some uploads use to cover both, and when you see it you cannot tell from the phrase alone how the work was split between the music and the words.
Arranged by names who decided how the music is set out for the instruments and voices, which is a separate job from composing it. The same song can carry the same composer and a different arranger on different versions. Produced by usually refers to who oversaw the recording of the song, but we want to be plain that the word is used loosely across the industry, and its exact scope changes from credit to credit. Treat it as a role label, not a precise definition.
Names come next. A line can list several people separated by commas, and the order is the uploader's choice rather than a ranking. A name followed by an @ and another name is the credit's own wording for a team, company or group the person is listed under. The upload usually does not explain it, so read it as written. It is also common for a performer to appear in a credit line. That tells you the role the person took on the song, and it does not say how much of the song they did.