Okay, no worries! This process might take a while, so you might want to plug both phones into a charger before you start.
To start off - how to get the Smart Switch App on your P9:
Setting up Smart Switch on your P9 (check the video attached)
Preparing Smart Switch on your S20 FE (see video):
Once this is complete, you'll be presented with options regarding what you'd like to transfer. Tick or untick as appropriate, and then continue.
The process is pretty much sit back and watch telly from this point!
Hope this helped, but if you need any additional details, check out this page Samsung's Smart Switch Page or comment again, and I'll try and do a proper demo.
@CrazyTom2k2 's Description is spot on and should be easily followed, however as the video does not seem to work I will put another one up here for those who are interested. @stan241165 may well have it sorted by now though.
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 4.0,Android 12 Official Version.