Can I select files using checkboxes?

Solution 1:

The checkboxes or something similar in Nautilus was planned a long time ago according to wiki: https://wiki.ubuntu.com/Ayatana/DoubleClick
But it was not implemented yet.

It is possible out of the box in Dolphin file manager but it's part of KDE, not GNOME/Unity.

Solution 2:

AFAIK, you can't make nautilus, the default Ubuntu file manager to use checkboxes. But you can install some other file manager that does.

I don't use alternative file-managers, but in this article list 20. Some of then can use checkboxes, although most don't by default. In those that are two-panels, you can usually use space to select more than one file.

There is also check Marlin. It's a nautilus fork, aimed at simplicity and ease of use, so they aren't going to use checkboxes, but it's quite popular.