Users will often download a dataset that is larger than the area they need. This will slow processing time and make the map look cluttered. For instance, you may download nationwide census tracts, but only need the census tracts in North Carolina.
To fix this in QGIS, users have 4 options:
After running the appropriate tool for your needs, you will get the following results:
If you have raster data, you will need to use the Clipper tool.