I am confused too, since I don't have any mobile phone, or GPS or any of that.

I have one computer on one bike, it's my Touring bike, I put it low on the Fork
off the handlebars to collect data and not play with all the time,
as All I really wanted was an odometer. it collected average speed too..

If you have topline Shimano or Campag brifters they have control buttons ,
for each companies own bike computer .
I have neither , my road stuff falls in C&V, now ,
though it was New when I got it.

may I recommend your Trek dealer, since they sold you the bike.
they want to make your riding experience the best.