Your ability to move financially is very restricted with a 401k depending on certain variables. This is a long term saving plan with a principal idea of keeping money in the market rather than having the ability to move it out of the account. You will pay applicable taxes and penalties if you withdraw cash prior to retirement.
An IRA account has similar restrictions in that you can not withdraw funds without a penalty and tax payments.
The main reason these have the restrictions is because you put money into them before taxes were paid. There are other reasons but that is the main one.
A Roth IRA is a retirement account you can have that has your money in it after you pay taxes. This enables you to invest your money without having to pay penalties and taxes, depending on certain conditions.
For you at your age, provided you do not have an existing retirement structure under way, and without a match from your employer, should forgo the 401k and get either a IRA or a Roth IRA.
The choice now is are you able to put cash away and not need it. Can you save money for retirement without at some point needing that money in hand. If you can save and not need the cash get an IRA. If you anticipate pulling cash out for some reason in a decade or two get a Roth IRA.
IMO, if you start a retirement account you should never touch it. The entire principal behind a retirement account is compounded interest. If you don't have cash in an account this is a minimal return. If you are good and don't touch that cash, after a decade or two you'll be looking at a decent start for your golden years.
I am in no way a financial advisor, nor do I play one on tv. Please research these types of accounts and if you are serious about saving I would consult a professional. At 150 - 200 a week you will make up ground pretty quickly.