Solution for the codes appearing on slider
When you use "Show Blog Posts in Slider" option, it's a common issue to see some extra codes over the slides. It's because the slider has been coded to get all the "excerpt" content of a blog post.
You can try to use the excerpt field for a better control & view of those texts. Navigate to "Posts > Add New" and see the button named "Screen Options" at the top right of the screen. Click it, then check the "Excerpt" box. Now scroll down the page and you'll see a text field has appeared which has the title "Excerpt". Write your "intro" text there and DON'T use the "!--more--" tag.