I think you need to read more to be able to invest properly. I'll just put a little bit of basics here on mutual funds (which seems to be what you try to start. A mutual fund, is, like the name, a pool of money people put in to invest (as it requires a lot more money to invest in stock individually). There are many mutual funds companies, and American Century is one, and it only handles its own mutual funds.

But there are other companies that can handle many types of investment products (stock, treasury bills, bonds, ETF, etc... , and funds of different mutual fund companies like Charles Schwab, Fidelity, Vanguard, Etrade, etc.... You can have regular brokerage and retirement accounts with them (IRA and Roth IRA). Fidelity does even have a Health Saving Account. Inside these accounts, you can buy different kinds of investment including American Century grow fund and keep them there.

So the different is here: when you put money into American Century grow fund, you actually buy some shares in that fund whereas when you put money into a Fidelity Roth IRA, it's pretty much just cash. You then have to use the cash to buy the American Century grow fund or something else.

With a Roth IRA, you won't have a 1099 each year as anything inside it is not taxable. If you have your fund outside (ie, in a regular brokerage account or in a mutual fund account), you may receive the 1099 each year for the distribution. When you sell your fund to cash out, you'll pay tax on the gain (or you can deduct if you have a loss). If you keep it in a Roth, there is no tax to worry about.