Selecting files / folders works fine for me in Pantheon Files by either:
Using and clicking the checkmark at the top left of an icon to select one or multiple entries.
Clicking and dragging the mouse on an empty area to make a rectangular selection area.
Pressing the control key (ctrl) before clicking on an icon also allows to select one or multiple files.
Running the following command in the terminal could solve this:
xmodmap -e "pointer = 1 25 3 4 5 6 7 8 9"
To make this persistent, edit your ~/.Xmodmap with a text editor either from the terminal:
or with a graphical text editor:
open files --> go to your home directory --> open .Xmodmap (a hidden
file) with a right click in "...
If you are using the daily unstable version you should check whether the schema io.elementary.files.preferences.single-click exists, in which case you should change that. The Tweaks tool is not guaranteed to work with this version.
This sounds like it is a problem with the compatibility of the trackpad.
Have you tried plugging in a mouse, and see if that works? Also, actually installing the system (as opposed to running it from a USB pen) will increase your chance at a fully working system since a bunch of software is installed from the web too (on top of the core stuff on the pen).