How do I root plants?

It depends on what you're rooting. Lots of plants can be rooted in plain water.

Not all plants are easily rooted from cuttings. The easiest are tropical perennials used as annuals in most of the U.S. Coleus, begonias, and pelargoniums are easy to reproduce with cuttings, and this is a good way to carry particular cultivars over winter. Do a search for "how to root cuttings of begonia semperflorens" for example. Look up whatever plant you want to work with.

It's really easy if your plant will root in water. Just cut some 4 to 6-inch stems, and remove any flowers and the bottom half of leaves from each stem. The plants only need 1 or 2 leaves while rooting. Place the stems in a glass or jar of water, making sure no leaves are at or below the water level. Set the jar in a warm room, but out of direct sunlight. Refill with water as necessary. New roots should be growing from nodes along the stem in 3 weeks, though some plants may take longer. When the roots are at least 1 inch long the cutting can be transplanted to a small pot, but the transplant should stay in a warm but shaded place.

When rooting in "soil" note that soil is not the best medium. There is a chance for soil-borne diseases to cause cuttings to rot. Most people use peat moss or coco peat (coconut husk fibers) to set their cuttings into. Both of these soilless mediums hold moisture while draining freely and are disease free. Water the plants you want cuttings from the day before you take them. Fill small pots with soilless medium and pre-moisten them. Take cuttings and remove most of the bottom leaves. Dip the bottom half of each stem in rooting hormone. Rooting hormone is not required for all plants, but tends to help. Poke a hole in the medium, insert the cutting, and firm the soil around it. Water the planted cutting just enough to settle the soil. Finally enclose the cutting in a plastic bag, or under a clear soda bottle with the bottom end cut off to provide maximum humidity. If using a plastic bag use wooden sticks (skewers) to hold the plastic away from the leaves. Each day you should open the container briefly so fresh air gets in, then re-cover the plant. After a week you can try the plant out of the container, but you may need to re-cover it if it wilts. During the root forming period make sure the medium stays moist, the air temperature stays warm and the plant has light but no sun.

Once again, these are general instructions. You should look up each plant for instructions on how to take cuttings.