There are 2 kinds of IRA....Traditional IRA and ROTH IRA.
Traditional IRA - Contributions may be deductible on your current return or not deductible. They grow tax deferred. When you take a distribution or RMD the whole distribution will be added to your other income and taxed as regular income. You don't get capital gains treatment on it. Unless you made any non deductible contributions.
ROTH IRA - Contributions are not deductible when you make them. But they grow tax free. So when you take a distribution you do not pay tax on it (not even on the growth). Unless you take it early and owe the Early withdrawal penalty.
Here are 2 IRS instructions
IRS pub 590A for IRA Contributions
https://www.irs.gov/pub/irs-pdf/p590a.pdf
IRA pub 590B for IRA Distributions
https://www.irs.gov/pub/irs-pdf/p590b.pdf
