Being signed in will give you the best results and the most options, but is not required.
The Search Bar at the top has two sets of options.
There are two other helpful options in this area:
After you perform a search, an Expand Your Search link appears.
For more information, check out
There will often be too many results. You can use the filters on the left to reduce your results.
After you search you have a lot of ways to filter your results on the left side of the page.