From the dashboard, click on Posts and then Add New.
Once in the editing area, you will be able to add a blog title and the content. Posts use the same block editor that is used when creating website pages. Click here to learn a little more about using the block editor. On the right, you will see options to add a categories, tags, as well as a featured image.
Once you have completed the blog post, make sure to click the blue Publish button at the top right of the screen!