-Extract the .ZIP file wherever, and place the .BSP file into: C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\maps -Go into the sound\custom...
You can tag anything on IndieDB on IndieDB, and all tags can be voted up/down by the community depending on their relevance.
Official tags, as well as up-voted tags will appear higher in the list as they are deemed the most relevant.
If you discover a page that does not have any tags applied, why not help out the community by submitting tags, or posting a comment with #tags in it, which will be automatically linked.