Attach a file to a post

I apologize if this is a simple question, but I have been poking around on my administrative panel for a little while now and have not figured this out. I did a search on this forum and it does not appear that a post on this has already been posted. I have the permissions set so that I, as the admin, can create an attachment on a post. However, I have not figured out how to do that. I see in the Administrative Panel that I can set up attachments in emails and messages, but I cannot find where to enable allowing attachments to a post.

I want to include a screenshot of something for those who read the post. The insert an image button on the editor menu requires a URL and this image is not on the web. It is on my computer.

Is there not a button to press by file in the upload image screen?

Is it the Host an image button? If it is, I will feel silly for overlooking it.

Yes

Do not feel silly.  It is easy to overlook something.

Thank you.