Are you talking about the geraniums that are actually pelargoniums, the red or pink ones that are used as bedding and in baskets? If so they won't last outdoors in the coldest weather, but will be happy inside - you can keep them on a windowsill in a cool room, a bedroom will do, and water them infrequently. Or you can take cuttings now and overwinter them in the house, keeping them growing. This is probably your best option. if you have different kinds its a good idea to label them so you know what they are before they start to flower again next year.

If you mean the mostly blue ones they are hardy and will last for years outside.

Agree with Steragram. I over winter some bedding pelargoniums in an unheated bedroom on the windowsill of a a south facing window.

I kept a white one of my uncle's growing for about 20 years indoors as I didn't have a garden.

When it got leggy I trimmed it down and put the cuttings in water to root.