Buying, selling and trading stocks in an IRA isn't all that different from conducting those activities outside of an IRA -- but with an IRA, you don't pay tax on your gains or get a tax break on your losses. If your IRA sells a stock investment and nets you, for example, $15,000 on a single trade, you don't owe any taxes until you start withdrawing the money. The IRS doesn't care if you change out your IRA portfolio every day.
Investing your IRA in mutual funds works much the same as investing outside an IRA. You aren't buying specific stocks as much as a basket of stock investments combined into a particular fund. If you're an inexperienced investor, you don't have to worry about making good picks of specific stocks. However, while you can switch to a different fund from the same broker, you can't trade individual stocks.
If your brokerage offers the option to buy individual stocks as well as mutual funds, you're free to pick and choose the stocks you want. If your picks don't pan out, you can then trade them as often as you think you need to. You can also opt for a self-directed IRA account, which offers a much wider array of investment options to switch between. However, you can't get any investment guidance from your broker, so it's a lot riskier.
The freedom to change stock picks as often as you wish doesn't make it a good idea. Day-trading with your IRA -- picking stocks and reselling them in a matter of hours -- is legal. However, it takes lots of knowledge and skill -- and lots of money in the account -- to buy and sell that rapidly without backing the wrong horse. If you don't intend to hold stocks for the long term, you need skill and experience to succeed.
If you intend to sell and buy stocks frequently, doing it inside an IRA offers tax advantages. A spectacular profit on a stock you've owned just a little while gets taxed at the short-term capital gains rate -- but if it's inside an IRA, you're off the hook. Instead, wait until you're older and start withdrawing money to pay income tax on your profits. The downside is that you can't take a tax write-off for bad picks, no matter how spectacular your losses.