What is Bitcoin?
Bitcoin is a digital currency. You can use bitcoins to pay for goods and services and there are exchanges where you can buy and sell bitcoins. There is no central bank and anyone can make new coins. 
Coins are created at a controlled rate and there will never be more than 21 million coins.
Watch this video for an introduction:

What is BitMinter?
BitMinter aims to make it easy for anyone to make bitcoins. Everyone should have the opportunity to take part in the currency revolution that is Bitcoin. BitMinter creates new bitcoins and helps the Bitcoin system process transactions. If your computer takes part in this work then you will get your share of the coins we create and the income from transaction fees.