First time for boys
Sex probably won't be great the first time but practice makes perfect! To start with you should practise putting on a condom (on your own) before you have full sex.
When the time is right and you are both completely ready to have sex, take everything slowly. Kiss, caress and explore your partners sex organs before penetration.
When you have an erection and have put on a condom, wait until your partner is ready for you to go inside and get them to guide your penis in the right direction.
Enter very slowly, talking to your partner to make sure it feels ok. You may orgasm very quickly the first few times, but with practise you'll learn to control you ejaculation by thinking of non-sexy things.
Some boys find it very difficult to 'cum' - usually because they don't feel relaxed. Others find sex does feel as good as masturbation.
Being open with your partner and talking to each other will make the whole experience better.