The easiest way is to prevent this is to enable the
Snap to option in Preferences so every clip will always directly touch the next clip when you place it on the timeline, regardless of the timeline's zoom level:
To remove existing gaps, there's no automated tool but I think the quickest way would be to zoom in quite a bit then click on a clip and hit the End key to instantly go to its final frame. If there's no gap, click on the next clip and repeat. If there is a gap, right-click and use one of the two
Remove and Move options: