Psalm 120 is the first of a series of 15 psalms each with the title, A Song of Ascents. The reason for this collection and arrangement is not precisely stated. The best explanation is that these were songs for the people of God as they made the pilgrim journey to Jerusalem and the temple at the three appointed feasts (Passover, Pentecost, and Tabernacles).
This psalm is all about the prayer and journey of an outsider.