Trim and Adjust Speed

[goddi]

Greetings,

Trying to figure the Trim function in this menu. As I play the video, I want to pause it to establish the beginning trim point. So the red triangle is at the point of the beginning trim position. How can I move the lower white triangle to where the red triangle is at? This has been the problem with the previous version. If I click on the white triangle to move it to the position of the red triangle, the red triangle will reposition back to the white triangle and I lose that set trim position. How do I get the white triangle to move to where I placed the red triangle?

And I have no idea how to use the other items, like Interpolate Frames, Speed Key Points and Speed. Is there a video on how to use them?

Gary