By default, Windows will use the index when searching to give you faster search results. The search index only includes your selected locations. These locations can be filtered for what file types (extensions), file properties, and file contents you want indexed.
The index uses the Windows Search service and runs as the Searchindexer.exe process in the background. The index will automatically rebuild and update for changes made to the included locations since the last index rebuild to increase search result accuracy. By default, the indexing speed is reduced due to user activity. If the computer is running idle, then the indexing speed will go back to full speed to finish indexing faster.
This tutorial will show you how to add or remove file types to be included in the search index and how they should be indexed in Windows 10.