You should contribute as much as you can to your company's 401k plan. At minimum, you should contribute the match amount that your employer provides. It's one good way to save for retirement. As Curt states, it's important to diversify your investment. Asset allocation will be important to your long term investment performance. Educate yourself on how you might want to invest your money, or get expert advice. A good starting point is to put your money into a target date retirement fund or an S&P 500 index fund.
Your goal should be to contribute 10% of your gross income. That's how much you need to save to be able to retire at your normal retirement age. Of course, you'll need to do that for the next 30+ years. If you're older than you'll probably need to increase your savings even more.
Start by talking to the HR folks and ask them for information about the 401(k) plan. Make sure they include the Summary Plan Document in the information they provide you. Take a look through the documents and most importantly start contributing to the plan.
Your employer might have some tools to help you decide where to invest your contributions. If your employer doesn't have anything to help there are some on-line tools that can assist. Remember, just like a lot of other things...don't put all your eggs in one basket. You will want to diversify your contributions across several asset classes or pick an age based fund that does that for you.
Hi Micha! You have lots of good recommendations here. In the past, I have noticed that those in the restaurant industry tend to not save very much for retirement. Of course this is not true for every server, and I am really glad to see you starting out in a saving mode. Ask if there is an advisor, whether in person or online, that can help you select investments to get started. Studies have shown that having an advisor can improve your investments by as much as 3%, so it's a good idea to get some individual advice.