Some people lay out a weed barrier around their plants. Some use black plastic(draws in heat) and some like myself use a wood mulch or lay out newspaper.
If you are going to use black plastic, you measure the area you want to cover, cut the plastic, and then make an opening in it where the plant will come up from the ground. You can then lay the plastic flat and plant right down through it.
Some people like to use small squares of black plastic around individual plants such as bell peppers like we do here in Maine where the ground doesn't get warm enough to keep the plants happy.
However, if you do choose to use the plastic, keep in mind that you want to limit how much of your garden you cover with it. It can tend to drive good things such as worms away and it can make the ground too hot in warmer climates. But small amounts around plantings is ok.
