Fast file indexing has become a best-practice in Linux since it’s an efficient way to search for files.
To Search the files via the index you need to index the files first, by using the command
$ sudo updatedb. Now that the files are indexed you can search them (or locate them) with the command
locate. For example if you’re looking for a
$ locate test.conf.
If you’re interested in a more in-depth discussion on indexing and finding files, you should check out this unix.stackexchange question (find vs locate), where user Warren Young explains what both do and which is better for what purpose.