The simplest native way is to use a rich text property bound to a rich text element, and then restyle a basic style like bold as your highlight.
This approach works in the designer since it doesn’t require any special script-processing, however unfortunately the component user would have to know “one paragraph only, bold the text you want highlighted” something like that.
Other approaches requires some creativity, and the highlighting will only appear in the published site.
SA5 has a Markdown feature which works well for this. You can tag the element in your component for markdown conversion, and then in your component property you can use markdown styling, like