This is a superscription that tells about the psalm. Some scholars say that this is part of the scripture and some say that it is not. (See "What are Superscriptions in Psalms" in [Introduction to Psalms](../front/intro.md).)
Possible meanings are 1) "song people sang while going up to Jerusalem for a celebration" or 2) "song people sang while going up the steps into the temple" or 3) "song whose words are like steps." See how you translated this in [Psalms 120:1](../120/001.md)
This is the beginning of a statement about what could have happened but did not. Yahweh really was on their side. (See: [[rc://en/ta/man/jit/figs-hypo]])