Create a page type called "Banner" with the following fields:
- Name - textbox, required (not displayed, system purposes only)
- Text - textbox, 200 characters (would steer away from an editable or rich textbox because it could mess up your markup if editor inputs invalid HTML)
- Image - URL selector field, 450 characters
Place a repeater on the page template you want the banner to show on. Set the repeater properties with the necessary values for path (./%), Top N (1), page types (custom.banner or whatever you named it), transformation name (custom.banner.transformationname).
Create a transformation with the markup you have and replace the static values with the values from the page type using
<%# Eval("ColumnName") %>.
Select the page you're displaying the banner on and click New page and add a Banner page type. Fill in the fields and save it. Should display your banner.
Technically speaking this is the simplest form of how Kentico is made to be utilized.