You can access the Materials dialog by clicking Manage tab
Settings panel
Materials, or from several other points in the software.

The Materials dialog displays only materials that belong to the selected class.

See Entering Search Text.
Revit searches each material for the specified text, checking the fields on the Identity tab of the Materials dialog. See Material Identity Parameters. If you selected a material class, Revit searches only materials in that class for the specified text. To search all materials for the specified text, reset Material Class to All.
The Materials dialog displays matching materials, sorted in order of relevance.