Very good thought. If you start at this age, you can build up a good amount
First thing is to estimate what would be your required monthly expense at the retirement age.
Then you can start saving every month. There is something called power of compounding. It means, you get interest on the interest earned.
In many countries, there are pension funds.
Another approach is to invest in a diversified portfolio, such as 50% equities related, 25% in Land
25% Gold etc.
One method which I found very good was to start systematic investment in mutual funds.