Get thee a digital scale first. You can buy a kitchen scale that measures in ounces, you don't necessarily have to get a postage scale. As long as it's accurate and measures in pounds and ounces.
It's super easy to ship with PayPal. Once you log in, find your transaction and click on "Print Shipping Label" Choose how you want to ship (First Class, Priority, etc.), fill in the weight and the type of package (you'll want to select Package/Thick Envelope) and any other options you might want (insurance, etc.) Click to the next page, and confirm everything. From the next page, PayPal will throw up a pop-up so you can print your label. I use normal white paper. Once it's printed out, cut out your label and tape it onto your envelope with CLEAR packing tape. Some people use Avery labels to print their labels onto, but to each their own.
I ship all my jewelry in a jewelry gift box in bubble mailers using First Class Mail and always with Delivery Confirmation using PayPal.
Good luck!