Lent is often observed with a fast of some sort. Traditionally, it is a fast of food, where the Christian will spend 40 days denying their body (whether a meal a day or a meal a week) and replacing the time with prayer and self induced discomfort to, in some small way, identify with the suffering of Jesus.
But, Lent can be observed in two other basic ways:
Rather than fasting food, you can fast fast-food! In order to remind you of the suffering and sacrifice Jesus made on the cross, you can give up something you enjoy: TV, eating out, caffeine or cigarettes. In its place, spend more time than usual in prayer and Bible reading.
Also, Lent can be a time of service for you. Find a way during Lent to serve people that cannot give back to you. In that way, you are identifying with the mission of Jesus.
So, when does the Lenten Fast end?
Glad you asked! It depends upon how you observe the fast. Many traditions break the fast on Sundays. The thought is that every Sunday celebrates the Resurrection. So, the 40 days runs to sundown on Maundy Thursday. Other traditions that observe a continual 40 day fast end at Palm Sunday.