What sort of exercises should i be doing for jiu jitsu?

Muscle strength is actually a huge part of grappling, i'm not sure who would tell you otherwise. Focus on Biceps (for pulling), Triceps (for pushing), and shoulders/Deltoids (help with defense). Do pushups, LOTS and LOTS of pushups. Both normal, and triangle pushups. When you feel good, do pushups. When you're tired, do pushups. When you're hungry, do pushups. Pushups, pushups, pushups. In addition, dips and pullups are great bodyweight exercises. Running is important for a well-rounded workout, but don't focus on it. Strength is what you need to work. If you want to use weights (which is fine, I always used them), focus on using light ones for lots of reps. It will provide you with better endurance. Also, you may want to try handstand pushups. You can youtube them if you're unsure what they are. FANTASTIC shoulder exercise.

Its just a safety thing, your instructor wanted you to know the seriousness of what you were doing but he didn't want you to be really embaressed so he made a little joke. Its really important you don't get hurt or hurt other when you train, especially when you're new. Notice how care youll be next class, thats how they want you to think. It's a good thing that you feel that way because you'll prob never forget. It may or may not be an illegal move in tourney's but stick with the moves you are shown in class until you understand the sport. Alot of dojo's especially BJJ are hard on the new students because the only want people who are serious, which is ok. go back to class, it sounds like you enjoy it, and it won't be the last time you get called out in front of everyone, but don't worry every beginer had to deal with it

Find a guy to have a training with at home. Try doing push-ups, working your hips and back. This will help your overall core strength. I also do some pull-ups as they help a lot when trying to keep your pal closed to your guard attacking with the armbar,

Stretch a lot! Stretch your legs and hips mainly, you will become more flexible therefore having a harder guard to pass, you'll be able to do crazy moves too!