Barbara,
Configuring dynamic pricing on ordering quantities differs based on whether you are selling or buying the product. If you are selling the product, you configure this in the price lists (as described by Ahmed). However, if you are purchasing the product from a vendor, you configure this in the product profile.
Configuring Dynamic Product
Pricing on Quantities Ordered from a Vendor– Odoo Online Version 9 SaaS 11
To view current dynamic prices for a given product:
Access the product profile (Products > Product in question)
Click on the INVENTORY sub-header under the product name.
Under Vendors, you will be able to input multiple different prices based upon minimum ordered quantities. You are also able to add multiple line items for each vendor and even give a specific line item a start date and an end date (e.g. promotional period).
To add more dynamic prices to this product:
Access the product profile (Products > Product in question)
In the product profile, click on EDIT on the top left corner.
Click on Add an item below the last submitted price item.
Select your Vendor, input your Minimal Quantity, and your Price.
You can also add a time frame for this pricing to be available by inputting a start and end date under Validity.
Click on SAVE & CLOSE
Please let me know if you have any other questions.