Most people are familiar with "vanilla" sex -- conventional non-freakiness that can be enjoyed by nearly everyone with waterproof flooring and stain-resistant slacks. You really could stop with that and be fine. Actually, nature kind of meant for you to stop there and be fine. But the human imagination is inexhaustible, and why should we expect the creative vision that invented astronaut ice cream and God to settle for standard penis/vagina fare? Once you have the basics down, you'll find there's a whole world of erotic variations for you to explore -- all it takes is an open mind and a junior-high-school (or equivalent) education.