How to put on minecraft capes?

I downloaded a cape from minecraftcapes.net. But how do I put it on now?

You have to buy one from optifine

I asked how to put this cape on but thank you

Kids don't check anything

Apparently neither do you.
Those are capes for a mod that is clientside.

Huh?

You have to install the mod from them.

I already knew that as I wrote

I see

And where did you write that please?

lul'