Vanguard: My favorite mutual fund company. Offers the cheapest mutual funds. Unfortunately, their IRA initial investment is rather high at $3,000. However, after the initial deposit, subsequent investments can be as small as $100 or less.
Other mutual fund companies include: Fidelity, T. Rowe Price, and many others. Every mutual fund company website will have links that give you a step-by-step guide on how to open an IRA account or mutual fund account.
Investing podcasts: If you like to listen to podcasts, here are some good ones explaining investing basics.