1st Base) French - Kissing. Usually with tongue.
2nd Base) Feel - To cop a feel, grope, or fondle.
3rd Base) Finger - Sexual stimulation using the hands. Oral sex could take place after this point.
Home Plate) Fuck - Sex, intercoarse.
Baseball is being used as a metaphor for intimacy. In baseball, if a player is on the bench they are not in the game.
"It was pretty chill, man. The movie sucked though." Evan replied.
"Did she let you cop a feel at the movie?"
"Dude, I'm still on the bench."
"That was like your fifth date. Shouldn't you be getting a little action by now?"
"Naw man, we're taking things slow."