Hi Amanda! Storyline 360 is part of a Articulate 360 subscription, so it's continuously updated with new features. Storyline 3 gets bug fixes and limited new features, but updates happen less often. In general, you should expect Storyline 3 to be behind Storyline 360, and there are some features, such as the modern player, that are exclusive to Storyline 360.
Here are some resources to help you learn more:
If you'd like to take a look at this file, you can grab a free trial of Articulate 360 here:
https://articulate.com/360/trialYou can compare the feature differences here:
https://articulate.com/360/storyline#compareYou can dig into the compatibility between Storyline 3 and Storyline 360 here:
https://articulate.com/support/article/Compatibility-Between-Storyline-360-and-Storyline-3-Project-FilesAnd you can always see Storyline 3 new features here:
https://articulate.com/support/article/Storyline-3-Version-History