Google sheets check if there is anything

Hello, I have a problem, I don’t know how to make a code. I need you to check if there is anything in Google Sheets, if you don’t have it it transmits an alert, if there is any value in Google Sheets it gives another command, I just don’t know how do I check if there is any value. In this case I wanted you to check if there is no line, if there is any line it does something else.

Have a look at this post.