To ripen quickly, put your green tomatoes inside a polythene bag with some ripe bananas. The ethylene given off by the bananas will hasten ripening.
Alternatively, wrap each tomato in newspaper or kitchen paper and place them in a box in a drawer inside the kitchen or other relatively warm place where they will continue to ripen over an extended period. Make sure you only store unblemished and unspoilt fruit as those with blight, rot or holes will not survive the slow ripening process.

You don't need whole bananas - the skins will do just as well! Just replace them if necessary when they dry up.