So I would like to know here how could I learn all the rules in this forum easily, quickly
Just read them again and again and memorize them:
Unofficial list of (official) Bitcointalk.org rules, guidelines, FAQand which is better for newbies to learn then posting or learn completely and then post ?
You are not restricted from making posts, but posting uselessly is not necessary. You can post when you feel you have something extra to add to the discussion and you are not simply repeating the points that have already been said by others.
Also, please read this one too:
Newbies - Read before postingand another question is - by maintaining clarity, how could i post in simple, clear, relevant and fluent manner ?
Isn't it simple? To stay relevant, you need to understand the context of a discussion and post accordingly. To stay clear, make your posts easy and understandable, and fluency can't be taught, it is up to you and your knowledge about how fluent you can be in making posts or writing your thoughts.