Have I cut the grass too short?

I moved into a house where the grass of our lawn was quite big. It was empty for a couple of months. I’m an absolute beginner, know nothing about lawn care, never mowed it.

I didn’t think it would be complicated. I ordered a basic mower from amazon and tested it. I’m not sure if I’ve done it right though, it looks brown after mowing. Have I cut it too short?

From what i understand it has a cutting height of 31mm.

Can someone point me in the right direction? Show I just hire someone to do it instead?