Portfolio pages can be created with the help of page templates
1. Log in to your WordPress Administration Panel (Dashboard).
2. Click the Pages tab on the right
3. On the next page, click the Add New tab
4. Type in your page name, for example Portfolio page
5. Under the Page Attributes, select a Parent for your page
6. Select your page template ( Portfolio full or Portfolio in the Page Attributes drop-down menu)
7. Under the Custom Field tab, add a new field called “category-include” (or just select it under the Name drop-down menu)
category-include – name of the category that is displayed on this Portfolio page (available only for the Portfolio page template) You need to use the slug of the category here (go to Portfolio -> Portfolio Categories and copy the slug from the tab on the right)
9. With that done, click the Update button
10. To create a new Portfolio with a new Featured image and content, chose Portfolio -> Add New from the left-side menu
11. On the next page, enter your new page title and put your content
12. Under Portfolio categories on the left select the category or categories.
13. Under Featured Image, upload your image (click the Set featured image link)
14. And click the Update button
15. To add the new portfolio page to the menus, go to Apearance -> Menus . Under the Pages on the right, select the page and click on Add to menu, then click Save Menu.
Feel free to check the detailed video tutorial below: