You don't pay taxes on the interest you receive from investments. When you withdraw them you pay capital gains on your capital gains.

You can put 4k into a Roth IRA which allows you to put in after-tax dollars and let them grow tax free. I think you can put over 10k into a regular IRA and that is with pre-tax dollars.

This doesn't take into account an SEP, Keough, or Simple. But first off if you're earning under 100k a year and under 30. You need to max your Roth IRA contribution each and every year.