In addition to John's answer, some 401k plans have a vesting schedule. This pertains to the company match portion of your account. So, like John mentioned, make an appointment to see your HR department to discuss your options. They will be your best resource to obtain the information requested.
This is a very broad question and you are not giving us much information. In short, it depends on what type of retirement plan you currently have. Speak with your H/R Department, benefits coordinator, or plan administrator regarding your plan. Pensions may allow a lump sum distributions or periodic payouts such as single life or life with period certain. A 401(k) may allow a lump-sum or in-service withdrawal if you are still working.
Funds can be rolled-over into an annuity (effectively a self-funded pension) or into an IRA. The insurance company or custodian can setup periodic distributions. Avoid commissioned insurance agents if you are leaning towards an annuity as some products carry very high fees and surrender charges. There are several fee-only and no-load annuity products available through fee-only advisors. Distributions from an IRA need to be carefully managed as you can run out of money if you have insufficient growth to compensate for distributions.
Taxes, taxes, taxes… with the exception of Roth IRA’s, distributions from pensions, annuities, defined contribution plans, and IRA’s generally get taxed as current income.
I would suggest extreme caution as this is a very complex issue and will be partly based upon how much income you need, what other resources you have available to you, your tax profile, and a host of other variables. Educate yourself or consult with a trusted Fee-Only Registered Investment Advisor. An advisor can help you navigate this mine-field.