Lent begins on Ash Wednesday and lasts through Holy Week.
Giving Stuff UpEdit
Christians like to give things up for Lent that they like; for instance, chocolate. Some very serious Catholics give up eating meat (which is great for the environment, though that's not why they do it). A few evangelicals take it one step further: they take periods where they do not eat at all during Lent.
At a lot of churches, they require that all flowers are removed from church; and make crucifxes more prominent. The priests and choir wear less adorned robes. In the Middle Ages, in order to make people sad, they stopped playing music all together in church.
This is an eample of the oppression that religion causes. Religious people are brainwashed into following rules that cause them suffering, such as giving up things that make their lives better. Atheism offers freedom from religious laws that restrict personal freedom and enjoyment.
The day before Ash Wednesday is called Fat Tuesday, or Mardi Gras in New Orleans. It's a day set aside for people to party and enjoy life one last time before Lent comes and they have to give up having fun. Although it was traditionally celebrated by eating pancakes; today, all most people do is party.
Ash Wednesday is the first day of Lent. At some churches, people go and have a priest draw a cross of ashes on their forehead. Some churches get these ashes by burning the palms used last year on Palm Sunday.
Even though it is widely observed, Ash Wednesday originated in the 10th century and is not based on biblical events. That does not stop evangelicals who attack "unbiblical" statements that are actually in the Bible (due mostly to the fact that both are in the Bible and it's unclear which one you should believe) from celebrating it.
Holy Week is the week that leads up to Easter and represents Jesus's suffering and death.
Palm Sunday is the day that celebrates how Jesus rode into Jerusalem on a borrowed (a.k.a. stolen) donkey. People waved palm branches at him and lay their coats down for his donkey to walk on. Despite this celebrity-like affection, the same people wanted him to die less than a week later.
Maundy Thursday is sometimes reffered to as "Holy Thursday." It represents the night of Jesus's arrest. First, he washes all his disciple's feet; then, they serve the first communion (This wasn't just your cousin's first communion, but the first communion. Ever). Then, Jesus ran off to pray in garden. To this day, nobody know what he prayed about, but it's clear that the prayer didn't prevent him from getting arrested.
Good Friday is the day that Jesus was nailed to a cross and died. Exactly what happened varies widely between different gospels. Mathew says that he complained, "My God, my God, why have you forsaken me?"  Luke says he was forgiving: "Father, forgive them for they know not what they're doing."  John seemed to realize that Jesus is a human, and wrote that he said, "I thirst." 
Lent ends before the stone is unrolled on Easter morning. Sorry.