There are two important reasons why young people drink alcohol at weekends.
A young person if her/his friends drink, she drinks too because it is the best way to make a lot of friends and you get on well with people. Although this isn't true: alcohol doesn´t make you nice, alcohol can make you stupid!
Another reason is because of shiness. They think that if you drink, you won't be shy and you will speak about anything, but under the effects of alcohol you don't think coherently.
Drinking alcohol is very bad, alcohol can damage your health. If you want to enjoy the evenings and have good weekends, you just have to be you. You can have a good time doing things such as going to the cinema, going to the park and playing cards...