If you go on ONE date with a guy, you are NOT in a relationship. But if you continue to see each other, then you are dating. But only meaning that you are going on a series of dates, still NOT a relationship.
But if someone asks you if you have a boyfriend, you could say "oh no, I'm just dating right now".
The word has different meanings depending on the context. But you're not in a relationship until one of you officially asks the other to be your girlfriend or boyfriend, and that person accepts.
For me, going on a date is like a pre-requisite for dating. You go on a 'first date' to get to know them better, then based off the results of said first date you decide whether or not to go for round two.