Tweaking appearance

I apologize, I am not finding training in the help files / documentation. I need help.

1. I want to allow someone to write a guest post.
(a) How do I show that the article was posted by someone else? (I must still approve the post.)
(b) How do I show an author bio for ONLY THAT POST?

2. How do I completely eliminate the “Related Posts” band?
(I am using the home page in masonry format, the navigation menu below the header, comment section, a sidebar and a footer. I DO like the “next post” and “previous post” links below the comments section. I do not use the “featured posts” or “slider” elements.)

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BY THE WAY: I get more compliments on the blog STYLE than I do on the articles. The STYLE is what YOU made. Thank you for doing so well!