An unsecured loan is simply a loan you get based on your good name and your credit rating. Often the interest rates are higher on an unsecured loan than on a secured loan because the risk is higher to the lending institution. If, for some reason, you are unable to pay back the loan and the lending institution does not get any money back. However, your good name and your credit rating are potentially ruined.
On the other hand, a secured load is a low you get when you put up some assets. The advantage of a secured loan is that you often get more money at a lower interest rate for longer repayment period that you would with an unsecured loan. This is because you have some assets to backup your loan. The lending institution prefers this kind of loan because if you find yourself unable to make payments, they can see your assets as an alternative form of payment. Because the risk to them is diminished they are able to provide you with more attractive loans at a better rate.