I'm a 21 year old guy and I wish to learn boxing in order to defend myself from adverseries and easily get out of sticky situations. But I'm a physically weak person and I have a leaner frame. Plus I'm of a timid disposition, so how should I start training at home, because I'm too shy to train with a coach.
After re-reading your post a few times, I would break this down to three separate areas.
(1) You want to learn a few boxing (punching) techniques to defend yourself, but (2) you also consider yourself a bit lean and weak. Lastly, (3) you prefer to train to train at home by yourself because you are a bit timid and too shy to work with a coach.
Fortunately you can (1) learn some basic boxing punches and footwork at home, but if you are a beginner, have no boxing experience and are too timid to use a coach, then you will have to rely on either written or video training material to show you the right basic beginner methods for punching and training. There a literally hundreds of books, video's and training DVD's on "learning to box" that you can use. Unfortunately if you use these alone without any supervision you may not practice the moves or techniques correctly. But you can always get the books and/or video's and try them. Here are a few links recommend:
UFN training videos
boxing training articles (awesome training articles)
killer heavybag workout
four basic punches
Now, Dan at some point in time - if you want to advance your boxing skills - you ARE going to want to start some basic sparring with someone else, to get use to defending or dodging punches and using foot work in relation to some else moving. This will require a partner, or coach. Sparring with beginners, without supervision by someone who understands sparring will usually lead to injury, ie...some getting punched and hurt unexpectedly. I really suggest that if you move to sparring, you do so under a trained eye.... But you can wait on this until you get in a bit better shape and feel more confident about your skills.
Second, if you are leaner and weaker, than you can work on basic body strength with strength building workouts. Many people join a gym to lift weights, but there are plenty of options for fitness and strength training for the home. Here are a few suggestions.
home cardio workout, punching, kicking
total body fitness workout
They are many more options to training boxing / self defense skills and strength training at home. I can't possibly put all the text, websites, books and video links here but if you know a gym or some people in boxing or martial arts you might also ask them their suggestions for training ideas.
Good luck to you and Keep punching and getting stronger!
thanks for you question. Sorry I've been traveling out of town and did not see this question for a while.