Does he mean the very opening effect? Looks like a Center Wipe transition to me.
Just apply that transition (under Wipes category)
change Edge Type popup to Solid Color (or not)
highlight the transition in the timeline and park the playhead over it
an arrow should show up in the Viewer that you can rotate to whatever angle you want for the wipe
Here is how you would keyframe the closing wipe at the end. To create the opening wipe at the beginning, just reverse this. Keyframe the first frame totally cropped to the center, to being fully opened some time later. To make it open horizontally, use the top and bottom Trim handles instead. Pretty simple.
- While on the first frame of the effect, click to activate the Canvas controls for Trim. This is the icon at the bottom left of the Canvas.
- Click the Keyframe diamond at the top left to create the first keyframe. You only need to manually create the first keyframe. Changes to this parameter anywhere else in the clip will automatically create a new keyframe on that frame.
- Notice the Crop section of the Video section in the Inspector will correspond to these on-screen controls. You can jump between the two for more precise control in other situations.
- Move the playhead in the Timeline down to where you want the image to be totally black.
- Drag the side handles to the middle, one at a time.
- A keyframe will be automatically created.
Here is an in between shot just for reference.
At the top right of the Crop section, in the Video controls of the Inspector, is the curled arrow "Reset" button if you get in trouble and need to start from scratch again.