Lent is a period of repentence, reflection and preparation for Christ's passion and resurrection. It is meant to be a period where Christians are extra sensitive to what Christ went through and try to improve ourselves through fasting and abstinence and alms giving (not just giving $).
Incidentally, there are misconceptions about fasting and abstinence. The Catholic Church only prescribes fasting and abstinence on certain days during Lent. Fasting means limiting food intake to two meals throughout the day, although a third, small meal may be eaten for strength maintenance. Abstinence, despite what most people think (no sex), is refraining from eating meat.
There are only two days that call for both fasting and abstinence, Ash Wednesday and Good Friday. All Fridays during Lent are days of abstinence. These are the "rules", so to speak, that are put out by St. Patrick's Cathedral (NY) every Ash Wednesday. Other Christian denominations have different Lenten rules, some stricter, some laxer.
Hope this helps,