Use the <img> element in the usual way. Images have max-width: 100% applied, ensuring they fill the entire width of parent element, as we’ve come to expect.
<img src="/img/brian-mcgowan-HiftPDiIVTY-unsplash.jpg" alt="" />
To give your image a caption, place your <img> inside a <figure> and use <figcaption> for the caption.
<figure>
<img src="/img/brian-mcgowan-HiftPDiIVTY-unsplash.jpg" alt="" />
<figcaption>
Photo by <a href="https://unsplash.com/@sushioutlaw">Brian McGowan</a> on Unsplash.
</figcaption>
</figure>