Your other post where you discussed wanting to be a SEAL, being a mechanic, etc. Had me mistakenly thinking you were a few years older. Sorry.
At 14 years of age....if you have a YMCA membership then take advatage of it and use their pool. If you have friends who are competitive swimmers have one watch you swim and offer some advice. There are tons of videos on youtube to use to your advantage.....no need to delve too deep into technique at the start, just t find some videos and begin by trying to emulate what good smooth swimmers are doing. Slowly look deeper into technique and make small changes incorporate those changes into what you do. The life guards are usually bored out of their skulls, so chat them up and seen if they can watch you and give you some tips.
If you dont have access to a pool to swim laps then you can walk, jog, ride a bike, skip rope, rollerblade, etc, to work on cardiovascular fitness.
Bodyweight exercises are good to do and dont require any specialized equipment. Here are a few to develop a routine out of....strive for perfect form:
Pushups
Crunches
Planks
Leg lifts
Jumping jacks
Hop and pops
8 count body builders
Burpees
Wall squats
Single leg squats
Calf raises
Lunges without weights/lunges with weights (use old milk our laundry detergent bottles filled with water...water weighs 8pounds per gallon)
Pullups/chinups (eventually)
Look up T,Y,I shoulder and upper back exercises.
Develop a routine of a few exercises, don't over do it at first, for body weight exercises start with 1 set of 10 to 15 reps....if you can do that with perfect form then add an additional set.....slowly increase your number of sets to between 3 to 5.
I highly recommend keeping a journal of your routine and particularly write down how you feel before, during, after the workouts....does not need to be detailed l, just some simple notes about the exercises how many reps, sets, how your form was, and how you felt.
Throw a bathing suit or shorts on and take a selfie. Take another 4 weeks later....dont bother with scales as they dont tell you much.
I highly recommend picking up an inexpensive heart rate monitor. If you cant find one for $25 or less then let me know and I can help you buy one...we can work something out via paypal but there is a sporting good store here where I live that sells basic models for th equivalent of $15 to $20. A heart rate monitor is like a personal coach on your wrist.....your heart rate is a direct reflection of the intensity your body is working at.
Start slow, journal what you do, make whatever you do a lifestyle change, and periodically look back at your journal to help you gauge your results.
-Z