How to find some question that I can perfect answer it?
To more easily find questions that you would be able to answer, you may look for the tags associated with the topics that you are interested in and know something about, or that you would like to know more about by reading questions and answers written by others.
You can search for a particular tag using
[tagname] in the search box, e.g.
[posix] substitution if you want to search for things tagged with
posix and containing the word
You may also automatically get certain questions highlighted or dimmed on the main page by adding "favorite" and "ignored" tags. Just click "edit" after "Favorite Tags" on the right hand side pane of the main page.