I overwinter my geraniums every year by trimming them back and you can either leave them in a pot or container but need to water them now and then. In the spring they will begin to grow again. Another way is to trim back well and dig a hole for them on the north side of your house, covering them with dirt. Just leave them there until around Jan/Feb. They should have shoots on them. You can then plant them wherever you desire. This sounds strange but it does work. Not sure where you live tho. A heavy frost may kill them outside but I have found burying them close to the foundation of the house they will be OK. When putting them in containers they need to be sheltered. This can be done by putting them in your garage. I have heard that you can also cut them back and hang them to dry in a place where they do not freeze, this I have not tried.
Have you tried putting How to Overwinter Geraniums in your browser to see what comes up??