You can generally use this website as it is, but you have to be aware of the following:
The background images and the avatar of the team member is taken from https://www.pexels.com. This means they can be used in your projects as is, without the need to consult anyone or include any kind of source in the source code. For more information, please visit: https://www.pexels.com/photo-license/
The logo is taken from Flaticon: (https://www.flaticon.com/free-icon/line-chart_126425#term=up&page=1&position=2) If you intend to use it in your project, you need to either download it as a premium member from their website or credit the author of the picture on the website. For more information, please visit: https://file000.flaticon.com/downloads/license/license.pdf
Please consider that the images included in this Gatsby starter are used as examples in order to show you how your website could look like, but it's best to use your own pictures and logos for your project.