Smooth Transition between clips

First, black space showing means you don't have the clips bumped into each other ... do you have Snapping enabled? The little upside-down U shape that is supposed to be a magnet above the control block and under the time code on the timeline?

If you tap the " + " key, you expand the timeline so your clips are wider across the sequence window. And it is easier to see when you have spaces between clips.

"Jumping" ... can be all sorts of things. Cross-fades, dissolves, and doing "L" and "J" cuts, where you keep the audio going from clip A but switch the video to clip B for a while (L cut) ... or the reverse, start the audio from clip B while the video from clip A is still going ... many techniques.

For all that, as Jim suggests, you need to simply study editing techniques. I always recommend looking at both what Adobe has for tutorials, but really ... to learn quickly & effectively, there's lynda-dot-com, a subscription service. Paying for a month or two of that will give you access to some excellent tutorials that come with demo content for you to work along with the training tutorial. You'll save yourself a TON of time if you learn first, THEN try to do.

Neil