To hit it off (with someone) means to quickly become friends with someone.
To get along well together.
When someone gets along really well with someone else.
1. I was nervous about my first date with Jenny, but we really hit it off!
2. You and Justin seemed to really hit it off!
3. We had similar opinions about politics, and the two of us hit it off right away.
4. A: How do you like your new business partner?
B: He’s great! We really hit it off. I think it’s going to be a great year for us.
be acquainted with, be of one mind, be on the same wavelength, click, fall in with, get along well, make friends, see eye to eye