I'm a 16 year old guy and I'm starting to gain muscle and this year I'm not doing a winter sport so I have a lot of time on my hands so I was wondering how much of weight should I use and how many reps

If you're looking for tone, not muscle gain, then a great fitness regimen (and it may seem ridiculous at first) is to, either right before you go to sleep or right after you wake up, start with one push-up and three sit-ups the first day. I know that doesn't sound like a lot, because it isn't, but the next day add 1 push-up and 2 sit-ups. And add the same number everyday. It'll add up quickly, and you'll be in great shape, especially if you include a cardio exercise, such as running a mile (or whatever you choose) every other day. Once you find the reps of push-ups and sit-ups too high, slowly work your way back down, get to a comfortable number, then go back up again. It's great for tone. But if you're looking to "body-build", this regimen alone won't cut it.

Thanks and I already know what to do to body build this is what I wanted to hear but what can I do in the weight room besides sit ups and push ups

Pilates is a great way to tone your body. You could buy a video or watch some online. YouTube has a lot of great videos too.

Lift weights.

In spite of what you'd think from listening to people talk, it's NOT easy to gain lots of muscle. Basic weight lifting like squats, deadlifts, bench press, dips, pull-ups etc will make you fitter and look better, and will give you functional strength, but you've got to be really hitting the weights hard and heavy for a long long time to see any visible increase in muscle.

I'd suggest lifting weights three times a week and doing cardio on three other days.

If you're trying to tone, and use weight to do it, the best way is low weight and higher reps. So if you were trying to tone your biceps, take a muscle building exercise such as Dumbbell curl, only use maybe half of what your 1rm(one rep max) is and do any where from 12-15 reps of that. Take 2-3 exercises from each body part and group them together until you have a training plan that works for you. Certain exercises are not able to be done by some people so it's difficult to suggest them. I'll post the ones I do as an example

Chest - bench press, incline and decline bench press, dumbbell press, dumbbell flies and machine flies

Biceps - Dumbbell curl, barbell curl, cross body curl, machine curls

Triceps - Overhead dumbbell press, skullcrushers, rope extensions

Legs - Leg press, leg extensions, calf raises, squat and hack squat

Also, something that I've learned that is almost always overlooked by many, drinking A LOT of water, it cleans your system out and really helps hydration which prevents cramping

I do at least 200 push ups a day right now... And at least 300 situps... Gym 5 days a week with 20 minute treadmill on 6 mph minimum. Bench press of 95 lbs minimum at least 30 reps. Dumbbells of 35 lbs minimum at least 30 reps. Barbell with 80 lbs minimum at least 30 sets. Pulls up twice a week at least 30 reps... I can't keep saying everything else I do... But I do all these everyday for 5 days. I rest 2 in between. I love working out and in 2 months I've seen great results! I mean really good. Like model status. Hopefully in 2 more I can reach my goal... I had no pack and now have a 4 pack and I see the other 2 sometimes... I have to keep working harder now! Let's goooo!!