I can see the feature "Top 4% this month" on my Stack Overflow profile page. When I click on it I can see the page having the details of lots of users including me.
What is this? is this the detail of the total reputation of the whole month?
It tells you that you are among the top 4% of users in terms of reputation gained for the current month. The link leads you to a ranking showing that you are currently ranked 1517th for the month out of all users, based on the 205 rep gained so far.
(I think it selects the ranking (year/quarter/month/...) based on in which view you rank the highest. So at some point the link might show your quarter ranking rather than the one for your current month should you have a quiet month.)
In any case, well done and keep it up I'd say.