I could only find:
https://trisquel.info/en/wiki/install-trisquel-windows-dual-boot-0
which would be useful if you need to shrink an existing Windows to create
free space for Trisquel.
This is really old but still helpful if the first link worked:
https://trisquel.info/en/wiki/full-disk-encryption-install
If you want to give more details no doubt someone here would help. For
instance, Is it a new drive?
I am in Trisquel 8 (alpha), on a 19.5 GB partition and unbelievably it's 3/4
full already. I have an encrypted 800 GB partition that I haven't started
using at all so soon can start moving music and stuff to it. Initially, after
install and getting most of my main applications installed, it filled about 5
to 6 GB.