In addition to using the presets, you can manually place the Anchor Medallion where you wish to Anchor your widgets. This is particularly useful in the event that you want to Anchor one Widget in relation to another Widget, an example of which is illustrated below.
In the image above, we have an Image Widget next to a Progress Bar Widget inside a Canvas Panel which is placed on another Canvas Panel. The Canvas Panel that contains the Image/Progress Bar is Anchored to the upper left corner of the screen. This could be used to represent a player character image next to a health bar for example.
Below the Progress Bar (as well as the Image, although it is not shown) are Anchored to the upper left of the Canvas Panel they sit in.
Suppose we wanted the Progress Bar to stretch but remain a fixed distance away from the right side and extend outwards by a certain amount. We can do so by breaking apart the Anchor Medallion by pulling on the left center piece as shown below.
You can now see in the image below that as we stretch the right side of the Canvas Panel, the Progress Bar stretches, but remains a distance away from the right side and extends outwards towards the center.
The problem now occurs that as we resize the Canvas Panel with our Widgets in them, the Image Widget does not stay in the position we first set it in (or in relation to the Progress Bar like we had hoped).
Instead of having the Anchor for the Image remain in the upper left corner of the Canvas Panel it sits it, we can move it manually to set a new Anchor point.
Above, we have Anchored it to the upper left corner of the Progress Bar itself. So now if we resize the Canvas Panel containing the two widgets...
The Image Widget stays a fixed distance away from the Progress Bar. Another problem though, if we push the Canvas Panel to the left instead...
The image becomes cropped off as we have not set a distance for the image to remain fixed at for the left side, we can do so by breaking the Anchor Medallion.
Above we have stated our Anchor point and how far we want our Image to extend away from the Progress Bar as well as the margin on the left side, so if we resize...
The space on the left/right of the Image remains intact, but what about the top and bottom? As we stretch the Canvas Panel down, the Image is no longer centered with the Progress Bar.
One more adjustment to the Anchor Medallion can fix that. Here we have stated how much we want the image to be pushed in from the top and bottom in relation to the Progress Bar.
And now as we resize the Canvas Panel in any direction, the Image resizes and stays in position in relation to the Progress Bar which also stretches.