You can, and should wear a pocket square anywhere you wear a jacket. Suit jacket, blazer, tweed jacket - they all go perfectly with pocket squares.
But how to fold these?
The first fold is so simple we will not offend you with an illustration. Just fold the pocket square in two or three, and put it in the breast pocket you jacket, so that the edge of the pocket square is barely sticking out. This is the most formal way of wearing it.
For other situations, may we suggest you use a more sophisticated way of folding, the envelope fold, or its even fancier brother.
We just received a nice selection of Italian pocket squares. Please see the selection here.