This article describes the steps to add a CMS block on all category pages, or just some specific category pages. You can also use this guide for adding CMS blocks on any pages.
Step 1. Create a CMS Block. If you already have the CMS block created, skip this step
Step 2. Add HTML in Content section
Step 3. Create a new widget
Step 4. Select the widget type CMS Static Block, and the active theme, or you can choose any type form the list.
Step 5. Set Widget title, and select on which website, store, or store view you want this widget to appear.
Click Add Layout Update, and select the type of category where you want the widget to be displayed on.
You can add multiple layout updates, to display the same widget on multiple types of pages.
Step 6. Select the container where the widget will be displayed. You can insert custom content in any container from your magento store available in below list.
Step 7. Go to Widget Options and click Select Block
Step 8. Select the block that contains the product description
Step 9. After the block is selected, click Save, and clear all caches and check on frontend. Below you can see the frontend result of the above example.