How do you load single player games? Through searching it's been said that you have to open the .ssf file with Spring, but when I do this it crashes and gives me this:

"Remote requested quit: Connection rejected: User name not authorized to connect".

Also another thing I don't get which may be connected to this problem is why my username in a single player game shows up as "invalid". Is that normal? Thanks in advance for any help.

Dunno about the invalid username thing.
Regarding loading, well, you can't save games effectively in spring, not yet anyway (which isn't a problem really since most games are multiplayer).

You can view replays if that's what you mean, just execute spring with the full path to the replay - also called demos and contained in the demos folder where spring is installed, or ~/.spring/demos on linux

Some games have single-player interfaces but basically what needs to happen is for spring to be passed a text file containing the parameters for Spring.exe to use to start the match (for example players, bots, map and game to use, starting locations etc.).

If your game doesn't have a single-player interface included, simply start up one of the multi-player lobbies and start a private game with some bots.

Do you mean loading a savegame, or starting a new game?

Loading a savegame (I'm playing BA). I noticed you can save games but was confused on how to load them. If that's not possible yet that's cool, just as long as I know I'm not missing something here.

It's sorta possible, you just need a special version of BA.