Sry I'm feeling a bit lazy right now..
In Premiere, go to Help - Contents. In the new window, click on Search and type in "rubberband" in the search field. Click on the grey Search button and click on a topic called "Using the Video Opacity rubberband". It should then tell you how to use rubberbands, which change the transparency levels between clips on video tracks 2 and higher. This is probably the best way to get two video clips to show simultaneously. You can also click on the "Using keys to superimpose and create composites" for other ways on creating transparencies. They're sorta complicated to use at first, but they offer more unique transparencies than the rubberbands (which are pretty ordinary). Hope this helps.
