To see where the points are, imagine the overlay being placed on a x-y grid. The bottom left corner will be at the lowest, furthest left point in the grid. This is anchor point 0 0. Alternatively, the highest point will be at anchor point 1 1 being the furthest from the bottom left corner. And you would find the center point of anchor point 0.5 0.5 in the middle of the 2 points.
There are of course points in between you can use by choosing an x and y coordinate between 0 and 1 for each as seen in the image below.
The anchor point is the point at which the overlay will spin around. This point’s location will not change its position on the screen.
So now to determine how the overlay will spin, imagine the overlay being a piece of paper on a table in front of you. Place one finger on your anchor point and use the other hand to turn the paper clockwise, never removing the paper from the table. This is how the overlay will rotate.
The image below is an edited version of that found on page 4 of the Placing & Animating Overlays guide in the guides section of the portal. There you will also find an animated GIF of how they rotate at the 3 main anchor points.
