Events = one-off gatherings. Spaces = your virtual HQ
Events are great for gatherings that have a specific start and end time. You can schedule them in advance, and each one gets its own URL made up of random letters and numbers. The event only opens minutes before it's scheduled to start, and it closes a few minutes after it's scheduled to end. After that, the link is no longer valid, and you will not be able to access the event.
Spaces are perpetually open (unless the host closes it), so they're great places to host more spontaneous meetings. You get to choose a custom URL, which makes the link easy for you and others to remember. There are no time limits, so you can feel free to jump in for as long as you want whenever you want. You can also set a passcode for your Space for added security.