1. Because if you have a plan early then you can start saving early, which increases the amount you will have. The future is also unpredictable
2. Set aside money over a set period (put aside money each month, year). You can set up a plan through your employer ie 401K, or set up an individual retirement plan (IRA). Your employer takes a percentage you choose out of your check each month (commonly 3%, 5%, %10, 15%). The money is taken from your paycheck before taxes therefore it lowers your income and you pay less in taxes. An IRA is similar to a bank account as you choose when and how much you put in over time. Both can be withdrawn at 59 1/2.
3. Compound interest essentially earns you more money for retirement. It can be important because you earn more than with regular interest.
4. Start balancing expenses, make a plan for retirement and practicing saving. It would also be beneficial to start setting aside money for retirement even if you haven't opened an account yet.
5. Make sure you can comfortably live off of your retirement. If you can't it would be best to maximize your retirement and savings, or consider working seasonally or part-time