Do not ship it until you get a payment that clears in your Paypal account, not in Sold Items. However, you wont actually receive the funds for 21 days. Thats Ebay's way of assuring you are legitimate. You can choose your own box or post office flat rate box whichever is cheaper, find packing material, even newspapers, you can print a label through Ebay and pay with Paypal or take it to post office and have them weigh it. You need a scale.

If your listing indicated that you use the USPS as your shipping method, you can take the packaged item to the USPS and pay for the postage. You need to get a tracking number for your package (if you use Priority Mail you will get a tracking number for no additional charge). Be sure to keep your receipt! When you get home, you need to indicate to eBay that you have shipped the package and add the tracking number.

Using whatever method you listed as the delivery method. Look at your own listing if you've forgotten.