This appeared on my screen, how do I get rid of it?

I suppose that this is/was your startup screen?

Shutdown.

Hold the shift key while starting until you see the startup line progress,

now it starts (very slow) in the SafeMode:

when started up completely, type your password, login, start Safari or another app, shut it down again, and select the apple icon on the left above, select "Shutdown".

After that start up normally.

expl. by starting fully in the SafeMode, a lot of caches are cleaned up.