Dogecoin is a fun, new and rapidly growing form of cryptocurrency. You can use it to buy goods and services, or trade it for other currencies (both other cryptocurrencies or traditional currency like US dollars). By far the most popular use the Dogecoin however is for "tipping" fellow internet-goers who are creating or sharing great content. Think of it as a more meaningful "like" or upvote, with real value that can be used all across the internet.
To learn more about Dogecoin the best place to visit is it's Getting Started Guide.