hmm i am a complete beginner as well and have been trying to do the same as you. Problem i find is many of the guidance and posts for volumio and linux in general are at a more expert level than i am. This is my limited understanding but i may be wrong!
I ended up buying 4" waveshare HDMI screen. The smaller screens use the GP10 pins of the pi. My understanding is that if you have a DAC or digital output for your music plugged onto the GP10s then you cannot then use the pins for a screen. So hence i got a HDMI screen as i have a HifiBerry Digital on my pi. If you are not using a GP10 soundcard then you can use a small screen.
I tried the 7" touchscreen plug in but it doesn’t work, and if I use the drivers from the Waveshare website it seems to crash linux. The screen uses the GP10s for touch. Some of the larger screens use USB connection back to the pi for touch and power control. From my reading of the GP10 pins, the screen touch does not use the same pins as my Hifiberry Digi so should work.
The only way i have got the screen working is by using the command line (i am old enough to have used DOS but still I do not understand linux syntax very well)
I needed to change the volumio config file. I have got the screen now working but just cannot get touch calibrated. If i use the 7" plugin touch works but it is not calibrated. If i use the drivers from waveshare it just crashes volumio.
So in summary, its not that easy for a complete newbie!