Featured image is a measured thing in your site for representing your post in a blog page, or any excerpt related things. So it is an important task to add Featured image in your posts to make it more attractive.
Generally WordPress provides inbuilt feature to add Featured image to posts. It does not require any coding or development knowledge for doing that. Please follow these steps for adding a featured image in your post:
1. Please go to Dashboard > Posts.
2. Edit the Post where you want to add Featured image.
3. Scroll to the very bottom of the page. On the right side you can see a place for adding Featured image.
4. Here you can Click on the Set Featured Image. It will take you to the pop up for uploading image.
5. You can choose your option for uploading image and Save that image.
6. Here is now what you want. Your Featured image is ready for your post.