An old desktop MAC--how can I make use of it?

I believe I bought it around 2010. It works beautifully except, of course, that it can no longer be updated. It has a nice, big screen.

Then I have my new little MacBook.

Does anyone know if there's a way I can connect the two so the monitor of the obsolete can be the screen while I'm typing on my laptop?

I did the Google on it and it's either 1. over my head or 2. doesn't look promising.

Thanks in advance if you have a good idea.