When you setup an account with any pay per click search engine advertising program your ranking for each keyword is determined by the amount you are willing to pay per click (your bid). The higher you bid, the higher you will rank.
You do have the option with search engine’s like Google to set a different bid price for each keyword. If you are a small business with a minimal budget to invest in pay per click advertising you'll probably want to take a guerrilla approach and bid low on keywords that your competitors have overlooked. If you've got a larger budget than that it can be best for you if you start with higher bids because then you can collect some conversion data and evaluate the direction your campaign should take a little bit faster.