I first posted this way back in 2010, and it still holds up well (dates aside). This comes from the good people at Aggie Catholic.

Everything you always wanted to know about Lent, but were afraid to ask.

For starters:

What is Lent?
Lent is a time when the Catholic Church collectively enters into preparation for the celebration of Easter. Lent originally developed as a forty-day retreat, preparing converts to be baptized at the Easter Vigil. Lent is a season of conversion. Conversion is the process of turning away from sin and turning to God. Lent starts with Ash Wednesday (this excludes Sundays, which are not part of the 40 days) and ends on Holy Thursday, the first day of the Triduum, the three holy days before Easter.
So why aren’t Sundays part of Lent?
This is because Sundays are always a day of celebration of Christ’s passion and Resurrection, so we celebrate on these days.
Does this mean I can “cheat” on Sundays?
Since Sundays are not part of the penitential season, you do not have to practice signs of penitence on these days. But, there is no reason you can’t do them either. If you feel you are “cheating” then it isn’t helping! There are some others that believe that Sundays are a part of Lent, but I do not agree with their take. Since the Church has some conflicting information (different documents state different things) I think you should do what you feel is best regarding the Lenten season and Sundays.

Why forty days and not some other number? Because 40 is a special number in the Bible. It signifies preparation for something special – as in the 40 day flood of Noah. * Moses stayed on the Mount Sinai forty days (Ex 24:18), * Jonah gives the people of Ninevah forty days to repent (Jon 3:4) – (there are many other Old Testament stories) * We also see this with Jesus, before starting his ministry, he spent forty days in the desert in prayer and fasting (Matt 4:2). So, as in the Bible, we spend forty days in preparing ourselves to rejoice at the Resurrection of our Lord at Easter. So, what is Ash Wednesday all about? Ash Wednesday is so named because this first day of Lent is where we are marked with ashes to show the repentance of our sins and mourning. This is also a Biblical sign that we live today. We can see this in several verses. * One verse is – “I turned to the Lord God, pleading in earnest prayer, with fasting, sackcloth and ashes” (Dan 9:3) * Other verses include: 1 Sam 4:12, Jon 3:6, Esther 4:1 and Matt 11:20-21 Today, ashes are still this same sign of repentance and mourning for our sins. They also represent our mortality. “I am nothing but dust and ashes” (Gen. 18:27). We started as nothing and our bodies will become dust and ashes after our death. Reminding ourselves that nobody escapes physical death, we look forward to eternal life.

There’s much, much more—read it all. You’ll want to print this out and share it with the gang at RCIA, or discuss around the dinner table.

Lent for Dummies