About applying transitions

To place a transition between two clips (centered on the cut line), the clips must be on the same track, with no space between them. As you drag the transition to a Timeline panel, you can adjust the alignment interactively. Whether or not the clips have trimmed frames determines how you can align the transition as you place it between the clips. The pointer changes to indicate the alignment options as you move it over the cut:

If both clips contain trimmed frames at the cut, you can center the transition over the cut or you can align it on either side of the cut so that it either starts or ends at the cut.
If neither clip contains trimmed frames, the transition automatically centers over the cut and repeats the last frame of the first clip and the first frame of the second clip to fill the transition duration. Diagonal bars appear on transitions that use repeated frames.
If only the first clip contains trimmed frames, the transition automatically snaps to the In point of the next clip. The transition uses the first clip’s trimmed frames for the transition and does not repeat frames from the second clip.
If only the second clip contains trimmed frames, then the transition snaps to the Out point of the first clip. The transition uses the second clip’s trimmed frames for the transition and does not repeat frames from the first clip.

The default duration of a transition, for either audio or video, is set to 1 second. If a transition contains trimmed frames, but not enough to fill the transition duration, Adobe Premiere Pro adjusts the duration to match the frames. You can adjust the duration and alignment of a transition after you place it.