How to move Photos library to external drive?

I think there are hardware problems on my old MBP 2010, and will bring it to Apple Genius Bar today.

Before I bring it, I would like to move/ copy Photos library (from this old MBP 2010) to external drive (G-Drive) in case this MBP does not perform at all. (It is shutting down if not plugged/ charged)

To move Photos library to external drive, as I know, just drag/ copy it to external hard drive. Then, when I need to use some of the pictures from external hard drive, how can I use? Especially on my New MBP 2017?

Thanks in advance for help!