These products include "selective" herbicides, "non-selective" herbicides, and "Pre-emergent" herbicides.
Selective Herbicides are designed to kill weeds without damaging plants around them such as your lawn. You can apply these products to your entire lawn and the weeds will die leaving a beautiful lawn. To choose the proper product, first be sure to choose a choose a selective herbicide designed to be applied to your type of grass. For example, selective weed control for Bahia lawns will kill St Augustine grass. Second, selective herbicides are typically designed to target a specific group of weeds such as "broad-leaf weeds" or "sedge-grass" so choose according to the type of weeds in your lawn.
Non-Selective Herbicides kill any plant (grass, weeds, shrubs, etc.) that they contact. These include glyphosate (Round-Up brand is the most well-known) that professionals use to kill weeds in flower beds, drive ways, and other areas you dont want weeds to grow. Some non-selective herbicides such as glyphosate must be applied directly to the weed and are neutralized when they touch the soil. This makes them safer to use around other plants. Other non-selective herbicides may remain in the soil for weeks or even months. These will prevent new weeds for a longer time, but they cannot be used anywhere near trees or other shrubs that may also uptake the product through their root system and die. Oak trees are especially susceptible.
Pre-emergent Herbicides typically do not kill weeds, but are used to prevent weed seeds from germinating. The best time to apply pre-emergents is before the weed season begins. Pre-emergents are safer for use around other plants and typically do not stunt growth of your lawn or shrubs as much as selective herbicides do.
Always read and follow label directions. Not all products are approved for the same areas of application or treatment of the same pests.