Blender 2.91 Tutorial for creating capes (you will need to install Blender first):
Open up the "Example Cape.blend" file included in the capes folder. This is the Physics Mod cape that gets used by default. 
Make sure when you model something that everything stays as QUADS. Triangles are allowed however the engine needs the quads to stabilize the
cloth simulation. Only use triangles for the contours of the cape shape. UV mapping as usual and make sure that you simply name 
the texture file the same name as the model file. Only .png is supported right now.
Now to the more interesting part, how do you fixate points of the cloth simulation so it doesn't fall to the ground? Vertex Paint!
Every vertex has a vertex color. Only the red component is important. When the red component is smaller than 1 the vertex is fixed
otherwise it is loose. You can see that on the example cape by changing to "Vertex Paint" and the Solid View (press "Z" -> "6").
To select individual vertices check "Vertex Selection" next to the Vertex Paint selection (in the top left corner). Now select individual
vertices by Shift left clicking them. Then select the appropriate color in the eastern panel (depending on if the vertex should be fixed
or not) and hit Shift + K to color the selected vertices. To select all vertices simply press "A" and to deselect everything "Alt" + "A".
If you have any questions left feel free to ask them on my discord: https://discord.gg/3ARYUrpdRg

Exporting the model from Blender:
First we need to apply the transformations to the model. Select it -> "Ctrl" + "A" -> All Transforms. Now we can export the model.
Select File -> Export -> Collada (.dae)
Make sure to set this up correctly. On the right side there are exporting options. Check "Selection Only". Check "Apply" under "Global Orientation".
Press "Z" under "Forward Axis". Press "Y" under "Up Axis". Go to the Geom Tab and uncheck the "Triangulate" box. Now enter a
filename and press "Export COLLADA". Make sure to also put a texture file with the same name in the capes folder (.png instead of .dae).