Place your cursor where you want the top of the image. 

Click the Add Media button above the blog tool bar.

Select your image file, add a Caption and an Alt Text (SEO purposes)  and click 'Insert Into Post'. Make sure you are legally allowed to use the image.  Make sure that scaled image is served in the smallest file size possible. Page speed plays an important part in how Google ranks your site.

Now that you are back to your blog post, left click the image. When inserting images into your posts and pages, you can have your text wrap around them. Just click on your inserted image to select it, then choose the alignment you want.