If you are driving, it is best to park in Parking Structure 2 which you can find by entering UCLA on Westholme Avenue off of Hilgard. You can get to Hilgard by making a left off of Sunset Blvd (if you are driving from the east) or by coming up from Westwood (a bit more complicated, but GPS should help you there).
As for getting to Humanities from Parking Structure 2, that’s a bit more complicated, but I offer you this truly awful map I’ve created that shows you how to get from “P2” to what is here denoted as “Kinsey Hall” but is now known as the Humanities Building. These maps don’t denote all of the walkways on the campus, so just trust the red line that I’ve attempted to draw from P2 to Humanities.
If you are taking public transportation, your best option is to take the 2 or 302 down Sunset Boulevard and get off at Hilgard and Wyton. You can also get off the Wilshire line in Westwood and walk up to Humanities but that is a longer hike.