If you have luggage or prefer to take the free shuttle to the bus stop look for the shuttle that says City Bus Center Employee Lot South. Then take the 3 bus to Venice or Santa Monica.
Or you can take the free LAXit shuttle to the uber/Lyft area and then walk to the 3 Bus Stop.
In this video I took the Santa Monica bus number 3 to Rose Ave and then walked 1 mile to the beach.
Also, if you want to take a second bus so you don't have to walk from Rose to the beach you could get off at Washington Blvd and then take the Culver City Bus #1 that goes all the way to the beach, 1 block from the Venice Pier.