Your instructor will ensure you are positively buoyant, or floating, at the surface when you enter the water. This will be done by adding air to your BCD using the inflator. Part of the familiarization process with your equipment is learning to inflate and deflate your BCD at the surface. Inflating (adding air) will make you float, deflating (dumping air) will help you sink, and making minor adjustments during the dive will help establish neutral buoyancy.
Most people float, especially with a wetsuit on; therefore, you will be using some weights (usually hard lead or soft lead shot) to help you sink. These weights must be secure but must also be easy to release in an emergency. Your instructor will demonstrate the best procedure to do both.
Your instructor will also 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.
Divers are concerned with 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 each phase of the dive.