Gardeners are able to force blooms indoors because everything you need is already in the cut branches. Besides the flower buds themselves, the branch contains enough food reserves to all he flower buds to expand. The indoor warmer temperatures and added moisture trigger or "force" the flower buds to expand.
When you venture out into the landscape to cut those branches for forcing, take them from the sides or backside of the plants so they won't be missed later when the bloom show begins outdoors. Cut branches that are manageable in a vase indoors.
When the branches are brought indoors and before they go in the vase, you will need to prepare the cut ends so they will not naturally begin to heal over. Take your favorite pair of pliers and actually crush the cut ends. Next, stand them upright in a pail of water keeping them at a temperature between 60 and 70 degrees to begin to force the blooms to open. Exterior walls of the home near the floor will be several degrees cooler and serves this need well. This will allow the buds to slowly open and keep their color better. Keep them out of direct sunlight for the same reason. Outdoors, the spring rains help soften the bud scales, allowing the buds to open easier. One trick from the nursery trade is to cover the cut branches with a moist towel until you begin to see color.
Depending on the kind of flowering shrubs and ornamental trees you are forcing, it can take as little as a week to as much as 4 weeks to force the bloom. For your efforts, bloom show should last between 7 and 10 days on display. To enjoy a continuous bloom show indoors until spring arrives, plan on cutting a few branches every week to replace those that are done blooming.
Forsythia and Amelanchier can be forced in just one week, Redbud, and Pussy willows take about two weeks and magnolia, Flowering almond, Honeysuckle and Crabapple, Lilac, Peach and Pear take three and four weeks respectfully. Simple flower buds are easier to force than compound flowers that contain many small flowers. Keep a simple log of how long it takes to force the blooms and how long they last so in future years you can have blooms any time you want. Avoid odors that go along with forcing blooms, by planning on exchanging the water in the pail every other day.