In Destiny 2 you will be given the responsibility to protect humanity from various alien races. You will find yourself up against not only these aliens, but also other players. The Destiny 2 servers have a pretty high capacity to hold all of the players, most of the time.
Unfortunately, sometimes your mission to save humanity can get interrupted when the servers act up. This can be quite frustrating but luckily there's a way you can check to see if the servers are down or if it's actually on your end.
If you're getting the dreaded error when you try to log on, have no access to your character, or the Tower, then chances are the servers are down. Before you begin blaming your own network and start troubleshooting on your end, check with Bungie. Thankfully, Bungie tries their best to keep players up to date with any maintenance or technical difficulties.