There are two ways how to access CPQ.
Create an offer through Product Management. In more detail read the article How to Create new offers?
Note! "Use advanced pricing plan" must be turned on under the offer configuration section.
After creating an offer, select the "View offers & Bundles".
Select the "Edit pricing plan".
After selecting the "Edit pricing plan" the section will be opened in a new window. Select "Create a new plan", choose an effective date, select "OK".
Note! One offer may have several pricing plans, but only one should be effective.
2. Another way to create a pricing plan can be done through offer configuration page: