It varies for everyone. It really depends on how much your hymen has been stretched already. If you play(ed) sports, horseback ride, use tampons, masturbate with penetration, all or any of those things would impact your hymen. So you could experience some pain to no pain at all.
Unless you have a rare medical condition, it shouldn’t hurt much at all. (Ie. If you have an imperforate hymen, that would make it very painful, but the condition only occurs in about 2% of the female population and you would know by now if you have that.)
The stretching of your vaginal walls takes some getting used to if you’re not using tampons or masturbating with penetration. That’s what makes it the most uncomfortable and it will probably take 2 or 3 times for you to really enjoy sex because your body needs time to adjust to the intrusion and expand itself the way it knows how to do.
The best way to make your first time the least painful, most enjoyable, is to do a HELL of a lot of foreplay, be soaking wet/aroused, and have an orgasm before any penetration occurs. Have your partner eat you out, or masturbate, or even hump them until you come. After an orgasm, your vaginal walls naturally widen and your muscles relax so it’s much easier for you to enjoy.
You could also have your partner finger you gently until you can feel yourself opening up and start experiencing pleasure.
If you’re tense, nervous, bracing yourself, clenching your muscles, that will only make it hurt more. Do it right. Relax. Take your time. Enjoy every moment that leads up to it because foreplay at this stage is far more important than the actual act of intercourse. Don’t worry about pain because it won’t be anything like you’re thinking.