If you want to have one and the same template for all the blog posts, you create one and insert it, then change the images and texts. If you want to have different templates, you will have to create different unique templates for each post.
I already created the blog using the WP posts page. I want to make the paragraphs less wide when viewed on desktop. I try to adjust the text through appearance>customize>css but I didn’t work. How can I do this?