how do I series , author that I know little about whether they write Romance, Mystery etc?

You could try the Fantastic Fiction website.  They list series authors, their book titles, and a short description of the book.
 

Also you can try the fictfact website. ( www.fictfact.com)

or Goodreads.com

i use a site called fictiondb.com it let's you see all the books in a series or books that are just connected by characters or author. it's very useful.

I recommend fictfact, too - their series listings are clear and concise, and they are very agreeable to adding missing titles of a series, or rearranging them if they have the books in the wrong order.

 I like GR but don't often use them to look up series. I love their yearly reading challenges and I use them to log my reading list.

I use fantastic fiction and fictfact a lot.  I like that I can keep track of where I am in a series on fictfact, but they only list series books.  Fantastic fiction lists all the books by an author including non-series--sorted be series and then by publication year.  I find both sites extremely useful.