select clips between IN and OUT points?

The function you are looking for is available as a hot-key, but it's not assigned to any key as default. To assign it to a key go to 'keyboard shortcuts' uner the edit pull-down menu, or press Ctrl-Alt-K (pc). In the search box below the virtual keyboard that appears type "Select In to Out" (w/o quotes).  When it appears in the left-side list, click and drag it to a key of your choice, such as F3. Note: if you click any modifier key (ctrl, alt, shift) on the virtual keyboard before you drag the command to your key of choice, then you will be adding that/those modifiers to your new hot-key (e.g. Ctrl-F3). The track target selectors on the left side of the timeline are still in play for this selection process.