Go to Adrian Bryant on YouTube! He is awesome.
You could do iso-holds (start at 2 mins and work yourself up - core workout), crunches/sit-ups/bicycle crunches/mountain climbers (core but also a bit of thigh workout - start at 2 mins), flutter kicks for legs, planks, lunges, push-ups, squats, wall sitting, burpees.
I’d say just work out at a comfortable pace, do maybe 7 exercises of your choice and do them for about 2 minutes each until you build up more endurance for them. It might be a bit of slow progress, but it’ll shave off some weight at a healthy pace. Another thing you can do is go for a walk in the morning and then eat about 15 minutes or a half hour later. Depends on how much walking you did (light walk do 15 mins, 2,000 steps or more wait about 30 minutes so your body will fast and burn some calories, eat a light breakfast so your body doesn’t/can’t hold onto the calories too much).
There’s an app called “Fitbod” where you literally enter all your info, your goals, and what equipment you have, and it makes a daily workout to follow along with, as well as shows you videos of the moves if you’re not familiar with them. Everything is tracked. I use that and really enjoy it. Good luck on your journey!
Rope skipping for cardio!
I personally started with bodyweight exercises for muscle building but quickly switched over to HIIT workouts. They work really well for me since they include cardio as well (I was doing HIITs for a few months and could suddenly run for an hour without ever going for a run when before I was dying after like five minutes. It felt amazing and was really fascinating). They can also easily be adjusted to very easy beginner exercises as well as really difficult ones so you don’t run out of things to do!
Also, I like Calisthenicmovement on YouTube since they show how to do exercises correctly whereas other people or channels don’t. I don’t enjoy their workouts as much though.
Wishing you all the best; I hope you’ll find something you enjoy!
Look up Tabata training; perfect for your bike!
Start by jogging or running 30 minutes every other day. Go at your own pace but dig deep for it every day. You’ll quickly build up stamina and find your happy pace and distance. Your metabolism will spike, and you’ll start burning calories fast. Watch your diet though. Don’t pig out and beef up. Hopefully, your body will naturally want activity on your non-running days, and these off days are when you do the push-ups, squats, climb mountains, etc., that have been mentioned elsewhere. Scale up duration, repetitions, intensity, rinse, and repeat.
Jump rope for cardio, push-ups, and crunches worked for me at your age. Fast results when you put your work in. I always heard Bruce Lee used to push as hard as he can against a wall for ten minutes.