How Much Will I Need to Invest?
Before covering in detail how much you'll need to save and how your retirement funds should be invested, let's determine how much money you'll need in retirement. As mentioned on the Establishing a Retirement Budget and Retirement Timing pages of this website, there are various rules of thumb regarding what percent of your pre-retirement income you’ll need, and these vary widely (50%-90%) based on your pre-retirement lifestyle and retirement goals/plans (see Setting Retirement Goals). Let's assume that after counting social security payments, you'll need to generate 50% of your pre-retirement income through other means. Let's also assume that that your investments will grow 6% annually and that you'll also earn 6% on your post-retirement investments. (Note that I prefer the 6% figure since it supports a rule of thumb that a $100,000 investment will yield $500 per month of income). With these assumptions, the table at the right of this page shows how much of your pre-retirement income you'll need to invest each month to have 50% of it available in retirement. 
Retirement Investing Overview
As previously mentioned, retirement savings can be made in pre-tax dollars into tax-qualified accounts [401(k)’s, traditional IRA’s, etc.] or after-tax dollars into Roth IRAs, regular brokerage accounts, savings accounts, etc. It's generally a good idea to have much or most of your retirement investments in tax qualified accounts. Money added to these accounts is not taxed until it is withdrawn, generally much later in retirement. Any growth in these accounts, through interest, dividends or asset appreciation also grows tax-free.
There are however many good reasons why a portion of your investments should be in after-tax dollars. Many of these investments can be converted to cash (income) at any time and any age without penalties. When money is taken out of these accounts, only the investment growth is taxed not the money put into the account. This may be especially important in retirement, when any additional taxed income could put you into a higher tax bracket.
The following tax-qualified and non-qualified accounts are most typically used for retirement savings/investments: 401(k)’s, IRA’s, Annuities, Brokerage Accounts, Certificates of Deposit (CD’s), and US Savings Bonds. Information on each of these investment alternatives is provided through the "Retirement Investing Links" on this page.