The sell prices tab on products contains all your sell prices for the product. There can be any number of sell price levels, though normally the main price levels are list, bulk1, bulk2, bulk3 and government.
At the simplest level, setting up a quantity break just requires that you enter a quantity in the quantity break column of the price level you want to change. If you want a bulk1 sell to apply when the customer buys 10 (each) of the item. Enter 10 in the quantity break of the bulk1 sell price. Take care that the prices is not set to update from the price book, by setting the ignore catalogue price changes checkbox on the settings tab of the product.
Price level can be setup in chains. So one lower price level links to a specified higher quantity break price level.
