I wish to learn to describe almost everything vivdly, how do I start?
easy! you read books! they can help you!
To be really honest, Blouen, this is something that comes from within the writer. Some are brilliant at vivid description and narrative, and some are hopeless. You have to analyse what it is that makes one good and one not so good, and try to use the same technique as the good one.
Why don't you try a series of short descriptions - like your boy walking down the street - and see what we think?