Lent begins with Ash Wednesday and ends with Easter. During Lent, we practice prayer, fasting, and almsgiving as a way to unite ourselves to the suffering of Christ and to prepare for the great celebration of Easter.
On Fridays during Lent, we abstain from eating meat. We can have fish and other seafood, and we can have foods made with cheese or eggs, but we abstain from eating foods made with beef, chicken or pork (or other warm-blooded animals).
Additionally, on Ash Wednesday and Good Friday, we fast. From the US Bishops website, these are the guidelines for fasting on those days:
For members of the Latin Catholic Church, the norms on fasting are obligatory from age 18 until age 59. When fasting, a person is permitted to eat one full meal, as well as two smaller meals that together are not equal to a full meal. The norms concerning abstinence from meat are binding upon members of the Latin Catholic Church from age 14 onwards.
Remember that these are minimums. If you can and want to do even more, you certainly may, keeping in mind your health and age.