Re: How to limit the scope of searching ?
You should be able to see the filters when searching in the community. It will appear once you hit enter and when the search results show. You will then be able to search by filters like "Location", "Labels", "Author", "Date" etc.
You may refer to the below screenshot.
Also, we have a help faq page in our community. It should be available when you click your profile icon and in the drop down as 'HELP'. It also contains some information about searching.