Oh that's cute, people still do bases?
1st base - kissing, often french kissing
2nd base -touching above the waist - never was clear whether it was over or under clothes
3rd base - someone has a hand down someone's pants
home run - SEX!
Then there was also more baseball terms
Bunt - masterbation
Inside the park home run-- Oral Sex
Relief Pitcher - Vibrator
Minor leagues - jailbait