'Best' is going to be a relative term to some factors you're going to have to decide upon. However, some good initial choices would be: do you have a retirement plan associated with your full time employment? Something like a 401(k) (may be a 403(b) if you work for the public sector)? Some nice things about doing this through your workplace is a) many times there are matching for a % your employer will put into that fund to encourage you to save and b) psychologically, if the money is just taken our of your check, it is easier to have never 'had' that money at all than to remember to transfer it on a regular basis.
If you don't have a 401(k) or similar, as mentioned in the comments, you can go to any brokerage and open an IRA account. Fidelity, TD Ameritrade, Charles Schwab, are all pretty decent so-called discount brokerages that will not charge you to open an IRA account, and transactions done with them online will be fairly cheap. You may also check your bank or credit union, as many of them have the ability to open such accounts as well.
Lastly RE:"Any way that would be help me save up money for retirement?", you have to commit yourself to saving each and every month. Think of it as paying yourself, first. It may seem daunting, but the first main step here is starting and sticking with it. Even if it is as small as $50 or $20/month to begin with, get in the habit of paying yourself first and learning to budget more retirement savings into the future. Make a budget and stick to it. And then get that money into a some assets that will grow over the next 20 years until you're ready for retirement. Right now, a most important asset you have is time: time to let your money grow. But you have to get some money in there to grow.
There are lots of help out there on budgeting, and then once you can start saving regularly, lots of help out there on good ideas what to invest that money in. This site is one of many, and if you have other questions, don't hesitate them.