The latter, for Roth IRA.^A^ If you haven’t set one up before, it’s pretty straightforward.^B^

^A^: There is such a thing as a Roth 401(k) which if offered should definitely be your top priority up to employer contribution match.

^B^: Vanguard is often recommended for simplicity and low fees. You can pick your funds when contributing. Typical starting funds are VTI and VOO (or the mutual fund equivalents with slightly lower fees, VTSAX and VFIAX).