The Advanced Pricing Matrix is an incredibly useful tool, that allows you to set prices based on different conditions; such as the different stores on your account, customer types, quantity ordered, and even between certain dates.
To begin setting these prices, you'll want to go to Catalog > Products > Edit Product > Pricing. Once on the pricing tab, it should look similar to this:
From here, you'll click "New Price".
Listed here are a brief explanation of these fields:
Store: You can choose the store you want this advanced pricing attached to.
Customer Type: Choose the type of customer you'd like to have access to this price.
Variant: Choose if you want this price on a specific variant.
Variant Inventory Item: The variant inventory group that this advanced pricing row applies to.
Start Date: The day you want the prices to take affect. (This is a great way to have sales on specific items for a pre-determined length of time)
End Date: The day you want the price change to end.
Starting Quantity: The amount you want the customer to order for the price to kick in. NOTE: If you want a product to sell for a certain price for 1-4 qty ordered, but different for 5+, you'd make a pricing rule for starting quantity at 1, then another rule for starting quantity at 5.
Your Cost: How much the item costs for you to make or purchase before selling.
Price: How much the customer is paying for this item according to the advanced pricing.
Variant Price Surcharge: Lets you set options on the amount a variant price would be.
Price Calculator: Attaches the pricing to a Price Calculator.
And that is all you have to do. Make a new record in the Advanced Pricing Matrix for each price change you want based on specific conditions, and the product will automatically change price pending on when/how/who is viewing the product.