When sexual exploration becomes goal-oriented, satisfaction becomes secondary, and we risk missing out on the various kinds of emotional and physical satisfaction sex offers.
"It is helpful to imagine sex as a journey," blogger wrote.
The sexual contact associated with each base has evolved dramatically since I was a teenager, although "home base" or "home run" has always meant intercourse, and "first base" has always meant kissing or snogging.
To use the expression correctly, you get or make it to a base, per my comment: quotation, if I interpret it correctly, they had intravaginal sex twice and then she performed oral sex on him.
There are, as the top comment on this question notes, four bases in baseball, and these have corresponding sex acts associated with them.
"I got to second base with that girl yesterday." "I didn't think I had a chance, but I made it to third base with her last night." One of the other answers has provided a nice link to the Wikipedia entry for baseball metaphors for sex.
That’s how I felt on a daily basis in the middle school girls’ bathroom. If one person touches or kisses another person’s breasts, for example, that’s considered “going to second base.” This has also been called heavy petting, feeling him or her up or making out.