Add up data from small areas to big areas in QGIS

Let's say you have a layer with lots of areas (like US counties) and for each area you have a number (in this case let's imagine it was vote count for different parties). How can you aggregate this up to the state level and create a state layer that adds up the numbers from each individual county and creates a total for each state? Well in QGIS you can do this using the Aggregate tool - take a look at the video to see how.