How do most goods dealers get started? Usually by selling one or two items, making a profit, buying some more and then selling them, too. Charity shops and car boot sales are great places to find hidden treasures, which you can then take home and sell on eBay for a lot more than you bought them for. This is a practice known as 'eBay flipping', and there's big money in it if you know what you're doing.
The 'knowing what you're doing' part is obviously the hardest part, so you'll want to take the time to know what's valuable and what isn't. Fortunately, eBay is now an app on your phone. Go to garage sales and thrift stores, see what's there, look what the same items sell for on eBay, and if you can make a profit, buy them and sell them on. If there's an option to buy in bulk, go for it and make more money!