There are special clothes designed for biking. They will be very helpful when going out for a ride, especially a longer ride. These clothes are designed to keep you warm in winter, and cool in summer. Most are reflective to keep you visible to cars.
Shorts: Cycling shorts can drastically change your riding experience. Most cycling shorts have a compression fit with extra padding in the butt are where you rest on the seat. This padding can increase comfort when going long distances. The compression fit reduces chafing and also makes you more aerodynamic. If you were to wear other pants, they might tend to slow you down because they catch the wind when you are going fast. They also have reflective stickers on them so that one can be seen by cars.
Shirts: Cycling shirts are not a necessity but they are nice to have. They are often referred to jerseys. These jerseys have several features like a half zipper. That way if you get hot, you can unzip your zipper, or vies versa. They also have a tighter fit to your body. This makes you aerodynamic. They also have pockets on the lower back. This way you can store items that you would need and it is designed so that it will be accessible, but not in your way. You can also get cold weather shirts that are thicker and warmer. I would also recommend wearing multiple layers in cold conditions.