If you have many references in your Mendeley library, it can be useful to search it to identify particular references.
To search your entire library, make sure All Document is selected in the left hand menu. If you want to search only those references in a particular group, select that group.
Use the search box at the top right of the screen, next to your name. The document details as well as the body text of any PDF papers in your library will be searched. Optionally you can restrict your search to one of five fields by selecting from the drop down list by the search icon. You can also search any notes you have made to references.
If you want to find all references with a particular tag, this can be done by using the Filter options in the bottom left pane beneath your library folders. Change the drop-down menu to Filter by My Tags, and then select the tag you are searching for. Hold down the Ctrl key to select more than one tag; this will return references which are tagged with all of the tags you have selected.
At the top right corner is a search box which can be used to find references within your own library.
Note that references in Groups are not automatically added to your Library.