Contribution Limits
The contribution limit is currently $6,000 per year, or the amount of your earned income, whichever is less. That's how much you are allowed to deposit into the account yourself. It doesn't include earnings (growth from the investments held in the account) or rollovers (transfers from other accounts). The limit is shared between Traditional IRA and Roth IRA, so if you contribute the maximum to one, you won't be able to contribute any to the other that year.
Although you contribute after-tax dollars, depending on circumstances you may be able to claim a tax deduction on your contributions which then makes it before-tax money.
Income Limits
You can contribute the maximum regardless of income. However, if you earn more than $75,000 (year 2020) and your employer offers a 401(k) plan, you won't be able to claim a tax deduction for your Traditional IRA contributions. If your employer does not offer a 401(k) plan, then you can claim the deduction no matter your income.
Whether you can claim the deduction or not determines whether your contributions are pre-tax or post-tax money.
Tax Benefits
Traditional IRA accounts are funded with pre-tax dollars (you make deposits using money withheld from your paycheck).
Traditional IRAs grow tax-free.
Traditional IRA accounts are taxed as income when you withdraw money. If you make the unfortunate mistake of withdrawing before age 59-and-a-half, you'll have to pay an additional 10% penalty on top of the taxes! (Do not ever do this if you can avoid it)
Recommended Providers
Vanguard is never a bad choice.
Robo-advisors are good if you are just getting started, or if you want a hands-off approach.
Recommended Investments
Index funds are the name of the game.
Target date funds are a great way to have a mix of index funds and bonds that gradually shifts towards the safety of bonds as you get older.