I’m a n00b so there ma be a better way to do this . . .
Click the TrueOS icon lower left - fifth icon from the bottom is the file manager (has a home icon)
That should get you started.
If you don’t like the built in file manager, there are several others you can install from the app cafe
dolphin, emelfm2, caja, mucommander, nautilus, pcmanfm, thunar