On a normal brokerage account, you pay taxes on the 100k of income. Any additional realized gains (sell of a stock) or dividends will create additional taxes on those.
If you put the money in a tradional IRA, you would be taxed on only 70k. The rest is taxed when you withdraw it (without penalty after 59.5 years of age). FYI this is a bad example since you can't put 30k in one year in a tax-advantaged account.
If you put it in a roth IRA you are taxed on the full 100k and it grows tax free and is never taxed again (assuming you don't touch it until after 59.5. FYI this is a bad example since you can't put 30k in one year in a tax-advantaged account.
