A 401k and an IRA are both tax-advantaged accounts that incentivize saving/investing for retirement. They both restrict withdrawals from the account in exchange for deferring or excluding taxes.
The quick rundown of the differences are the following: you have more flexibility investing in an IRA, you have a higher contribution limit for a 401k, and your employer potentially matches contributions in your 401k (basically gives you free money in the account). But let’s go into some more detail.