combine parts of texts from few cells into one

Hello,

I know that we can manipulate text in cells a bit. I am trying to receive an PO number combined from different parts of texts that are in 4 cells.
I don't really know how to start off with it.

I have attached a sample if anybody could help me in explaining how I can manipulate the text that would be great.

If you guys have any idea how and if it can be done please let me know.

Thanks for reading it.
Simon