Equipment and Gear
You don’t need to go out and spend a lot of money to start walking, but there are a few things that you should spend a little more money on at first (i.e. good walking shoes is a must)
Good Pair of Walking Shoes
Don't just go out and buy the shoes that your best friend wears or have the prettiest colors (even though that is a bonus). You need to find a shoe that fits your foot, gait, size, and miles you plan walking. You should go to a specialty running store that can recommend a shoe based on your gait and other physical aspects.
You can wear loose comfy workout clothes and socks you own, but it is wise to stay away from cotton as it may cause chaffing. Once you get into walking more you can look for more technical or breathable material.
T-shirt, a long-sleeved top, or a tank top/singlet.
Your top should be a wicking fabric, not cotton. Cotton will trap moisture, get heavy, and chafe more. A wicking material will draw the moisture away from your skin, making it easier to get rid of excess heat and also offering some protection from rain.
Shorts or running tights
Running shorts should be light and also made of wicking material.
If it's colder, you could wear some running tights or women could wear Capri’s
I would avoid sweatpants as they will have the problem of not being made from the right material, therefore will get heavy and cling when wet, and be too hot when it's warm.
Don't have to be anything special, but you should still stay away from cotton. The key to socks is protection from blisters, so you need socks that will help get rid of moisture, and fit well. Look for Dri-Fit or moisture wicking socks.