Snow boarding and snow skiing are 2 different sports that share many things in common. Unless your friend is a professional instructor, I suggest you take some lessons from the local ski school. This should save the frustrations and the friendship for both of you. Learning to ski is a set of new skills and they take time to learn. As much as your friend wants to help, the expectations are usually too high and the student teacher rapport is hard to develop. Your nervousness and learning curve will be your own and it is usually faster for you to get a pro to do the teaching. Have your friend at the resort, let them ski on their own while you are in class, the added expense is cheap compared to loosing a friendship. Let them advise you about clothing and skin protection, listen to your instructor about the on snow skills. Fit your boots tight around your foot and ankle. Only your foot and sock in the boot, the heel must be full back in the shell and when buckled, it must not move around your foot. Boots too large is the most common problem for inexperienced skiers, and probably for snowboarders as well. Stay on the beginner slopes the first day or 2. Get in shape before you go, jump rope 15 minutes a day for 2 weeks before you go, practice balancing on one foot, then hoping to the other. Do this several times a day, walk and jog to get your endurance up to a reasonable level. Have fun, make some new friends, and some old ones. Skiing is as much a social sport as a snow sport.
40+ years teaching skiing.