How to setup a folder in Mint 22 on another partition.

I've searched multiple time on the web but can't seem to find an answer to my question. 2TB drive with multiple partitions, one group includes Mint22 (swap,EFI, /). I have 3 unused partitions (all ext4) - I'll use 2 of the partitions to install/try 2 other distros along with Mint22. The 3rd and last partition I'd like to use to build a structure on it where I can copy & paste data/docs/downloads/miscellaneous files I work with on the other distros.

How do I create the folders in this last partition. Mint22 has already used it for their Timeshift so that structure is already there. Sorry for being a noob but I gotta start somewhere.

TIA!!