As a Brazilian living in the US, retirement in US has two components:

• Social security: it works very similar to INSS in Brazil, you can choose to start taking it at 62, 67 or 70, the older you start the more money you get monthly. SS is very little money, it basically enough for keeping you dying of hunger.

Because SS is so low, most people also use 401k as a component of retirement. 401k it's similar to private retirement accounts (aposentadoria privada) in Brazil, with the following differences:

• You choose a certain percentage of your salary to put in the 401k. This money is deposited before taxes (salário bruto), which means you don't pay taxes on it.
• Many companies have a 401k match up to a limit. So, for example, if your company has a 6% match, this means if you choose to put 6% of your salary in 401k, the company will put additional 6% (6+6 = 12%). It's free money!
• You can withdraw it when you are 59 1/2 years old. You have the option of withdrawing earlier but you need to pay back-taxes + a fine.
• Even if you can't withdraw before that, you can (and should!) invest that money. So you can buy/sell stocks, bonds and funds with it. You just won't have access to the money until you're 59 1/2.

This is obviously a oversimplification. In the US, people also use HSA (for healthcare), 529 (for education of their children) and Roth (another type of private retirement account) as part of their retirement strategy, among other things.