How do I use the TWRP Recovery img as a tool?

[Kralj Karlo]

I get stuck at this step of the installation.

> Then the TWRP Recovery img is used as a tool to flash all other
> components to the target device.
https://docs.plasma-mobile.org/Installation.html

That is, once I get to the TWRP Recovery img, I don't know what to do.
For context, I don't know anything about Android really. (And that is
why I like the idea of Plasma Mobile!)

Could someone elaborate on this procedure?