One way to do this in the storyline is to find an obvious and easy "sync point" in both related clips. The "out" clip should be layered over the "in" clip. You can move the clip over the storyline by selecting it and typing command-option up-arrow (a gap will replace it's position in the storyline).
Select one of the clips and move the playhead to the point you want to line up and type M to set a marker.
Select the other clip and move the playhead to its line-up point and type M and set a marker.
The markers should be attached to the specific individual clips.
Turn on snapping (or hold down the N key if snapping is off) and move the upper clip in the direction to line up the two markers. They should snap (and you'll see a vertical yellow line drawn through both markers)
Trim the upper clip like you want it, select the entire clip and type command-option down-arrow to move it back down into the storyline. Select what's left of the gap and delete it.
If you need to "fine tune" the markers for lining up the sync points, double click on the marker and while the popup is open, you can type Control - , (comma) to "nudge" the marker to the left or Control - . (period) to nudge the marker to the right. (nudging is by frames.) Repeat snapping.... etc...
HTH
