I'm a 20 yrs old boy with polio in my right leg, and due to this fact I never tried to learn to ride a bike.
But now I want to give it a go, but since I have no one to teach me (I have no friends or family), online videos are my only options. Please point me to any videos or websites that can teach me how to ride a bike.
My biggest problem is that I can't do the balancing as the entire right side of my body is very weak. Also please recommend my first bike; I want it to be light-weight.
I think the consensus in recent years has been to not use any kind of training wheels when learning to ride a bike. For young children there are balance bikes which don’t have any pedals or drivetrain by design. I guess as an adult you can try to “imitate” such a balance bike by removing the pedals and possibly the crankset from a normal bike and lower the seat so both feet can reach the ground comfortably. You then “walk” while on the bike and try to balance longer and longer until you can lift up both legs and still not fall over.
I’d probably try this with a cheap, used, slightly smaller bicycle with relaxed seating position first. Get a proper bike once you’ve learned to ride and know that you can actually do it. This way you are also able to actually test ride the new bike before you buy it.
If it turns out that your disability makes it hard or impossible to balance and/or stay on the bike you can look into tricycles. Recumbent tricycles are fast (small frontal area for low drag) and fun to ride. Unfortunately they are quite expensive.
In many countries there are groups that have an interest in helping people with disabilities get into cycling - e.g. https://wheelsforwellbeing.org.uk/ . I would suggest such an organization if you have one local. If not, the resources offered by these groups in other countries might be helpful.
With electric bikes becoming popular, all sorts of alternates that were too heavy to be practical become an option, have a look around for ideas (The above web site has some listed).
Try to work out where you would like to get to, are you aiming to be able to ride a standard bicycle, or is the aim to have a machine that gets you mobil. How much (secure) space do you have to store it, ideally inside.
Cost is probably the limiting factor in what you can do. Look to see if there is support in your country that will help fund a bicycle, this could be thorough government agencies, local charities and NGO's etc. A local support organization might be able to help.
If all else fails, get in touch with you local bicycle club, and a bicycle coop if you have one.
I foresee two possible issues with your situation:
The first issue is easy to overcome. You just make sure you lean a bit to the left when stopping and you use you left leg. Your leg will be almost straight when touching the ground, so it may not be an issue at all. For me landing on the left leg is a habit and I always do it. I only put the right leg on the ground when I loose balance to that side, that happens sometimes because I do not put any effort in to avoiding it.
The second issue is also easy to overcome, just buy a bike with more gears. Then you can always keep the pedals moving fast enough to provide most of the power with your right leg when going up hill. I would recommend 7 or 8 gears, that should be enough. Bikes with more gears usually have two handles to change gear, that can be confusing when learning several new things at the same time. If you like technical stuff you can also buy one with 28 gears, it's not a huge deal to have two handles for gear change.
I know training wheels are generally not recommended, but if you really cannot hold yourself up with your right leg, even when it is (almost) straight, you may want to consider having a big training wheel on the right side only.
One last tip, find a safe place to practice. Not all countries have safe bicycle lanes.
As indicated in the comments, try out a recumbent trike, this will work for people who are so weak in one leg that they can not learn on an upright bike or even trike, but can be more comfortable for people who can learn to use other cycles.
Recumbent trikes are available for people who can not use one side of their body at all, if you have limited use you can mostly use one standard as factory made or at most with the brake handles all worked with your strong hand.
Depending on the location you might be able to get one from the support groups also already mentioned.
There are also sit-up trikes, which are likely to work for you, but you will still need to balance your body, while a recumbent trike has much more support as you sit in a kind of chair.
This is a link to a wikipedia photo of one recumbent trike.
Another option is a bike or trike where the handlebars are also the pedals. I've seen one or more in use. You pedal and steer with your hands.
Or one where you pedal with hands and steer with a foot or other body part. Haven't seen one, but it would surprise me if no one has ever built such a thing.
