The X between the clips on the sequence opens a transitions box where many choices are shown. 
If you don't see that X, expand the timeline with the slider at the bottom-right of the window. 
Or use the TRANSITIONS button on the toolbar.
https://www.google.com/search?client=firefox-b-1-d&q=Videopad+transitions
Check out the tutorials linked at the top of this forum. And in Videopad itself, click the ? at the top-right.
Use <ctrl-F> to open a search window at the bottom-left to help find topics of interest.