Help with American Speak

Help the English girl?

Bases. 1st base. 2nd base. 3rd base. Okay, so you come back from a date and you say, "I got to 3rd base." What does that mean? Is there some sort of unwritten understanding of what each base means? I assume 1st base is the best and means you got to have sex?

Soooo, If you came back from a date and you never even kissed, for whatever reason, even though you both clearly wanted too. Would that be missing 3rd base? Or are their more bases?

Am I making any sense?