Help! How to make consistently sized letters

I have just been put on a font creation assignment at my internship but am completely new to Glyphs and font creation. I need to make all of my letters consistently sized and spaced out but have no idea how to do this. I have watched multiple tutorials but they have not been too helpful so any guidance is greatly appreciated.

You can try scaling them to the Same height. Select the outlines, and type in a vertical size in the grey info box. 500 is usually the x-height.

How did you make these letters?

I am unable to select more than one outline at a time, is there a certain window that allows you to select more?

And the letters were copied straight from a font illustrator and my instructions were to alter them in Glyphs

Since each of them needs to be scaled differently, you will have to select them one after one, and scale them to the correct size.

Or, make them the right size in Illustrator already, before you copy and paste. There is a tutorial for that: