After an extraction occurs, there is an extraction site, which is essentially an open wound in your mouth. This wound needs to heal over before anything can be done with your jawbone, or with the empty, once tooth-filled socket of bone that the extraction site leaves behind. This extraction site needs time to heal before it can handle an invasive surgery without any damage to the nerves, bone, and surrounding supporting tissues. This can only be assured if the bone and other tissues are allowed to heal properly before undergoing a serious surgery.
There are instant dental implants, which can be inserted right after the extraction takes place. These implants have a different threading and the screw is somewhat different as well, making it possible to undergo implantation directly after extraction, but only if it really is done in the same session. If a few days have passed since your extraction, you have to wait for the full healing time before getting your dental implant inserted. These dental implants are still under clinical trials, but they are available on the market, and have just a slightly higher rate of failure then regular dental implants.