How do I set the scale for a floor plan?

Hi, I'm new to 2D (or any kind of CAD), and I'm trying to create a floor plan and site plan for planning permission application. I need to print on A4 paper at a scale of 1:50 and 1:00, with dimensions in metres. I've been trying for days, going through tutorials and changing parameters but have got so confused that I've forgotten where I started from.

Additionally, I am using a Mac and all the tutorials refer to the Windows setup which seems to be functionally different.

I would really appreciate some help!

Kate