I spent quite a long time to understand everything.

(it) took me a while = (the task) required time (significantly long time) to get it all figured out. = to understand, or sometimes to work out how to make things work (does not alway mean understanding, but sometimes just capability to function)

I got it now.

It depends on the context, but I'd say : I spent quite a long time to understand everything.

What does that mean?