Product prices are managed through Price Lists. You can read a further explanation of Price Lists here.
In your web console, navigate to the main menu item 'Products', and then to the drop down menu item 'Price Lists'.
On this page you'll see all of your current Price Lists.
Double click on your chosen list to edit, or highlight and press the Edit button in title bar. You will get a dialogue box containing the Price List configurable options.
At the bottom of the list is an option for Price Entries - Press the Edit button next to this.
You will then see a list of your products and their prices.
Navigate to the product to which you would like to add or change a price. Double click or highlight and press Edit in the title bar. You will see a further dialogue box where you can change the price of your product.