Is there a match? Are you able to save >$6500 a year?

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401k is investing but with tax advantages

You can start it with just a couple % , so it’s not like a big commitment

If your employer matches your contribution then absolutely! (That is, if you contribute 4% of your pay to the 401K, then the employer will contribute another 4%.) That's the easiest money you'll ever make. Contribute at least up to the maximum that your employer matches.

Now while the money you contribute is yours forever, there could be fine print on the company match. For example, if the company contribution only "vests" (meaning it becomes permanently yours) after 3 years, and you don't expect to keep working there for 3 years, then it might not be such mandatory, but it's still a good way to invest tax-free.

Anyway the usual rule is to contribute up to the match if at all possible, to get more of your employer's free money.

If there is any match, hell yeah. At least the minimum to get the full match.

If no match, I’d probably throw in a few percent just to establish the habit, but wouldn’t go crazy.

If there is a company match, never leave free money on the table. Usually the average rate of return is 8% which is likely more than your car and student loans. Plus compound interest at your age will give your great returns by the time you are at retirement age.

Unfortunately, No.

If there's no match then a 401k and IRA are interchangeable, if you'll be saving less than the IRA limit you can just stick with an IRA for simplicity.

Quick hack for anyone who wants to choose their risk tolerance in Digital Advisor:

When you get to the risk quiz, just do the opposite of what you should do. So when they ask “would you risk $1 for $5” set it to the minimum value, and when they ask “would you risk $1 for $1.25”, set it to the max value.

The quiz will end up confused, and allow you to select whichever risk tolerance you want. If you don’t do this and the quiz assigns you a risk tolerance, you can either go with that risk tolerance, or pick one of the adjacent ones.

open it now and put in the minimum for a full match

It sounds like maybe there is a possibility that you're not sure whether you actually qualify or not. I would talk to your HR department, a lot of times these sorts of things slip through the cracks as part of the on-boarding process, in the case when full-time employees are the norm. In other words maybe the plan is assuming your full-time and maybe HR didn't correct them.

Contribute fully up to the match amount right now. Tonight. Don't wait until tomorrow. Free money, are you kidding me? Easy answer.

But no match? Screw it -- you have to get rid of your debt first.. We are assuming you already have healthcare with an HSA plan you are filling annually, you have a Roth with a highly-diversified ETF like VTI that you max out based on your earned income, and you have an emergency fund fully fleshed out for 6-12 months of your budget. You have a budget, right?

Pity about that student debt and car loan. Does it charge more in interest than your investments might earn? That should be your answer (after filling the HSA, but before you do the Roth).

And withdrawal limitations. If you'll need the money before retirement, a 401k is not the right way to go.