Your instructor will ensure you are positively buoyant, or floating, at the surface when you enter the water. This will be done by ensuring you have sufficient air in your BCD. In addition, your instructor will show you how to inflate and deflate your BCD at the surface in order to descend or establish positive buoyancy.
Most people float, especially with a wetsuit on; so to help you sink, you will be using some weights to assist your descent. These are easily released in an emergency, and your instructor will demonstrate the best procedure.
Your instructor will show you how to achieve neutral buoyancy, and some time will be spent ensuring you are happy and confident with this skill. Buoyancy control is the most important skill to learn. It is key to safe, comfortable, and enjoyable diving.
Below is an illustration of the three states of buoyancy: positive, neutral, and negative. You will learn more later about how your equipment helps you achieve the buoyancy that is right for that part of the dive.