How to create a proposal and what will be limitation to create a proposal?
I have checked on "AREA51" for create a proposal but didn't get solution. This question may be repeated.
I'm not sure what you are asking about regarding "limitations", but you can read the 'faq' to learn about the process:
To submit your proposal, go to the listing page (http://area51.stackexchange.com), pick a category to the left, then scroll to the bottom and click "Propose a new site".
Please let me know if you need anything further.