Having an IRA and knowing what to do with it are two different things. When it comes to choosing your retirement investments, IRAs can be more complicated than 401(k)s -- simply because many IRAs have access to the full range of exchange-traded securities. It's far more challenging to pick investments from thousands of stocks and funds versus the 20 or so funds available in most 401(k)s.

Thankfully, you're in the right place to find some direction. Read on for an introduction to six exchange-traded funds (ETFs) and how each one might fit into your diversified IRA portfolio.

One-stop shops: Target-risk ETFs

If you want an easy, low-maintenance portfolio, a target-risk ETF may be the right solution. While many ETFs hold all stocks or all bonds, target-risk ETFs hold a stable mix of both.

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That creates some efficiencies for you as the shareholder. You can be diversified across and within asset classes, while holding only one fund. Plus, you don't have to rebalance every year to keep your equity-to-bond mix where you want it to be. That mix is called asset allocation, and the fund manages it for you.

You can identify appropriate target-risk funds by their asset allocation. Your desired asset allocation should be a function of your timeline and risk tolerance. If you have a longer timeline and higher risk tolerance, you can hold a high percentage of equities. If your timeline is shorter and you are risk-averse, a more even split between equities and bonds is a better strategy.

Here are two target-risk ETFs from iShares with different asset allocations.

1. Aggressive allocation ETF

iShares Core Aggressive Allocation ETF (AOA -0.59%) holds 80% equities and 20% bonds. This composition is suitable if retirement is still a few decades away. In strong markets, this fund should deliver good growth. It has exposure to the S&P 500, mid-caps, small caps, and emerging and developing markets.

The fund's expense ratio is 0.31% (with a reduced net expense ratio of 0.25% through 2026). It has produced average returns of about 9% over the last 10 years.

2. Growth allocation ETF 

iShares Core Growth Allocation ETF (AOR -0.58%) is the previous fund's more conservative sibling. The core growth allocation ETF manages to 60% equities and 40% bonds. That's a nice mix of assets if you are risk-averse or you're hoping to retire within the next 15 years.

This fund also holds small to large companies, plus international stocks and bonds -- though the weights of these assets are quite different than AOR's.

AOR's expense ratio is also 0.31% (with a reduced net expense ratio of 0.25% through 2026). The fund has produced a more modest 10-year average annual return of about 7.7%. That's to be expected since the asset allocation is on the conservative side.

Two core equity ETFs

You can also manage your own asset allocation directly by pairing all-equity ETFs with fixed-income ETFs. You can get super specific with this strategy. For example, you might hold a dividend fund, a real estate fund, a developing markets fund, etc. But it's generally smart to choose a broad market fund as your core equity holding. Below are two popular choices.

3. S&P 500 ETF 

SPDR S&P 500 ETF Trust (SPY -0.66%) tracks the S&P 500 (^GSPC -0.71%) index, which includes 500 of the largest public companies in the country across a range of economic sectors. The 10-year average annual return of the index is 14.38%. The fund's performance is just behind at 14.24%.

Fund expenses account for most of the performance gap between the fund and the index. In this case, the fund's expense ratio is 0.0945%, which is about two-thirds of that performance gap. The remainder usually comes from timing differences and transaction costs as the fund shifts its holdings to match changes to the index.

4. Russell 3000 ETF

iShares Russell 3000 ETF (IWV -0.59%) mimics the results of the Russell 3000, an index that represents about 98% of the U.S. stock market. The Russell 3000 index includes the S&P 500 companies, plus a larger group of smaller and mid-sized companies.

This fund doesn't hold all 3,000 stocks in the index. Instead, the fund uses a sampling approach to replicate index performance. Holding fewer positions is a strategy to reduce expenses for shareholders.

IWV's expense ratio is 0.20% and its 10-year average annual return is 13.6%.

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Fixed-income ETFs

It's a good idea to moderate the risk of your equity funds with at least one fixed-income fund. The safest choice is an ETF that holds U.S. Treasury debt. Or, you could go for higher yields (and higher risk) with a corporate bond ETF. Here's a look at one of each.

5. Short-term Treasury ETF

The Vanguard Short-Term Treasury ETF (VGSH -0.05%) portfolio consists of about 90 U.S. Treasury bonds with an average maturity of two years. Shorter maturity debts will yield less than longer ones, but they are less sensitive to rate changes. Rate changes inversely affect bond pricing. When interest rates rise, bond prices fall and vice versa.

VGSH has an expense ratio of 0.05%. The fund has delivered 10-year average  annual returns of 1.16%.

6. Corporate bond ETF 

Vanguard Total Corporate Bond ETF (VTC -0.27%) tracks the Bloomberg Barclays U.S. Corporate Bond Index, a benchmark for high-quality U.S. corporate debt. The portfolio is weighted toward intermediate maturities, but also includes short- and long-term debt.

The expense ratio is 0.05%. VTC was launched in 2017 and has returned about 5% annually since then. That compares to the index's growth of 5.2%.

Diversify within and across asset classes

These ETFs can help you grow your IRA safely because they're well diversified. By holding a variety of equities and bonds, you shouldn't feel the full force of each position's price volatility. That makes investing for retirement far more tolerable -- and more profitable, too.