When a person decides to invest, can you invest though a bank into a company like wal mart or mcdonalds?

a broker is a 'sort of bank' that trades for you on a stock exhange. once you have a broker account. you can trade freely in any stocks that are traded on the stock exhanges they give you access to.

mcdonalds and wal mart are both public companies so yes, you can invest in them.

The cheapest thing I've found is Computershare.com.If you want to buy say Walmart or B of A they buy the 1st share for you at the going rate plus a $50 fee. After that you can set up monthly investments ( $50 per month minimun I think ) or you can buy more if you want. you are buying directly frpm the company,no brokerage fee. Selling is pretty cheap.
Check out DRIP (direct reinvestment program ) on line, I found out about from Motleyfool.com

You invest through a broker, not through a bank. You can easily invest online by starting an account with one of the online brokerages (e*Trade, Sharebuilder, Scottrade, etc.)

you need to open an account with a broker, some banks have them others don't.