Adding info from one cell OR if that cell it's empty, from another

So, I am compiling a report that has similar information on for example, column A and B.

Here's what I am trying to do:
In a separate column, gather the data from column A and if Column A is empty, gather the data from column B.

Please let me know if you need any more examples.

Can anyone help me?

Thank you,

Thx!!