Click on the desired character symbol and press “select”
You can now paste it into your text box in Revit or AutoCAD.
Back in the Character Map dialog box, you will notice when you select some symbols, in the bottom right corner, you will see the relevant keyboard symbol shortcut: Alt + ****. Ensure you are using the numeric keypad for the shortcuts (right numbered section of the keyboard and not the numbers across the top over the letters). The symbols I tend to use a lot:
° (degree symbol) = Alt + 0176
² (squared symbol) = Alt + 0178
³ (cubed symbol) = Alt + 0179
Thanks Shane for reminding me of this. I did to use this system when I was first using AutoCAD 12, but I had totally forgotten about it.