A transition moves a scene from one shot to the next.
Generally, you use a simple cut to move from shot to shot, but in
some cases you might want to transition between shots by phasing
out one and phasing in another. Premiere Pro provides many transitions
that you can apply to your sequence. A transition can be a subtle
crossfade or a stylized effect, such as a page turn or spinning pinwheel.
While you usually place a transition on a cut line between shots,
you can also apply a transition to only the beginning or end of
a clip.
By default, placing one clip next to another in a Timeline panel
results in a cut, where the last frame of one clip
is simply followed by the first frame of the next. When you want
to emphasize or add a special effect to a scene change, you can add
any of a variety of transitions, such as wipes, zooms,
and dissolves. Apply transitions to the timeline using the Effects
panel, and edit them using the Timeline and the Effect Controls
panel.
In most cases you don’t want transitions to occur during the
essential action in a scene. For this reason, transitions work best
with handles, or extra frames, beyond the In and Out points set
for the clip.
Transitions are available in the Video Transitions and the Audio
Transitions bins in the Effects panel. Premiere Pro provides many
transitions, including dissolves, wipes, slides, and zooms. These
transitions are organized in bins 
by
type.
For a video tutorial that shows how to apply and adjust transitions,
see the Adobe website.
For a video and a print tutorial on making transitions, see the Adobe website.
You can create custom bins to group effects any
way you’d like. (See
Work with bins.)
