The electricity in your homes comes to you from the electric company by way of alternating current. Your car uses direct current. Your computer adapter takes that alternating current charge from your wall and converts it to direct current to be used in the computer. So, whats the difference? Well, simply put:
Direct Current is a current which flows in one direction.
Alternating Current is a current which flows in two directions.
Okay, you good? Didn't think so. That doesn't exactly answer the question, does it? Well, there is a very famous history behind this known as the War of Currents. We won't go into it here, but check the informational and you can learn about it.
The important thing to know about it was that Thomas Edison introduced DC and Nikola Tesla introduced AC, and they had a battle royal until it was basically determined over time that both had their advantages, but AC was more fit for large scale distribution. The main drawback of direct current was that the further from the source, the more the current dissipated. The short presentation upcoming will give you a good understanding of the whole thing.