en_tn_condensed/phm/01/01.md

Paul, a prisoner of Christ Jesus, and the brother Timothy, to Philemon

Your language may have a particular way of introducing the authors of a letter. Three times Paul identifies himself as the author of this letter. Evidently Timothy was with him and probably wrote the words down as Paul said them. Alternate translation: "I, Paul, a prisoner of Christ Jesus, and Timothy, our brother, are writing this letter to Philemon"

a prisoner of Christ Jesus

"a prisoner for the sake of Christ Jesus." People who opposed Paul's preaching had punished him by putting him into prison.

brother

Here this means a fellow Christian.

our dear friend

The word "our" here refers to Paul and those with him but not to the reader.

and fellow worker

"who, like us, works to spread the gospel"