To force indoor bulbs is to trick them into flowering early. Forcing it through a false, shortened winter and enjoy indoor spring colour. For Christmas flowering most bulbs will need to have been started in September however early October is not too late to start some off for late winter, early spring flowering. Forced bulbs need their roots to be kept moist yet well drained. Put some grit or crocks in the bottom of the pot and then mix more grit, plus some coarse sand, in with your potting compost. Plant the bulbs close together, pointy bit uppermost, leaving their noses peeping above the compost surface.
After planting, water your pot and going forwards, do not allow it to dry out. Place your pot in a cool room, shed or garage and keep in the dark. Covering the pots with newspaper will achieve darkness. During this time the roots will develop. The exceptions to this are amaryllis and Narcissus Paperwhite - they need the cool but not the dark. For maximum impact you want the bulbs all to flower at the same time. This means sticking to one variety rather than planting a mix as you would in outside pots. Once the leaves start to form move the pot to a warmer location in bright but not direct light. The bulbs themselves have stored food and so there is no need for them to be given extra. All they will need is water. Once flowering has finished your bulbs can be planted outside. Allow the foliage to die back naturally and your bulb will flower again next year. But at the normal time! Except for amaryllis, bulbs can only be forced the once. With care amaryllis can be brought back into flower every year for several years.