Ok, still here? This is where the work starts. First you need to establish whether your theme has css code for a horizontal rule.
Rather than plow through the themes stylesheet, go to one of your pages or posts and click the text editor, then insert <hr> somehwere in the text. Click on preview and see if a horizontal rule has appeared, if not it's most likely you need to insert some code.
To do this, go to your dashboard, click on Appearance>Customize>Additional CSS, then copy and paste the following code,
hr {
margin-top: 1em;
margin-bottom: 1em;
margin-left: auto;
margin-right: auto;
border-style: solid;
border-width: 4px;
border-color: #352ece;
}
Now go back to your text editor and if the <hr> tag is still there, or if it isn't, reinsert it, refresh your page or post and you should see this:
Don't worry, I'll be explaining how to change it later in the tutorial. Just make sure that your theme allows customization of the stylesheet.