For the first one, I’d say it’s a form of masturbation. As far as how to feel comfortable about it, it helps if you know what you like and you have “practiced” masturbating on your own. Your boyfriend has a lot of helpful suggestions, which is great, but remember you don’t have to do anything you don’t feel comfortable with. It can take time to learn what you like and what you don’t like, you don’t have to try the entire karma sutra in the first week. There is plenty of time to figure it out!
Being “tight” is normal if you’re just starting out. As you continue to have (safe) sex, you will find it gets a bit easier. The vagina is an incredible part of the body, it’s capable of expanding far enough to push out a babies head and a penis is wayyyy smaller than that. If you feel tight and uncomfortable, it’s usually because you’re nervous and clenching your muscles or because there isn’t enough lubricant. Take your time with foreplay, relax and stock up on a good quality lube – which you can buy from the supermarket. We have some info about lube here that may be helpful.
‘Stretching it out’ is really not something that needs to be done. Like @ElleBelle mentioned, the tight sensation can usually be because the female is not fully relaxed or fully aroused, and there are loads of reasons that this can be the case so it’s not anything to worry about or feel that you are not doing right. I’ve had this happen plenty of times in the past with a new partner or when getting ahead of myself. I would just suggest taking your time and letting your partner know what would make you comfortable rather than either of you attempting to force the moment.