If you just want to build a single, quick web page, then Spark Page is your best choice. Spark Page is completely WYSIWYG, which stands for What You See is What You Get, and you can't access any of the computer code behind a Spark Page, even if you wanted to do so. The advantage of this simplicity is that you can build a web page and share it (often through social media) with almost no preparation or tutorial. The disadvantage of having Spark "do all of the thinking" and coding for you, is (1) it is awkward to build a website with multiple pages in Spark, and (2) you only have a single option for the structure of a Spark Page, namely: an unfolding vertical scroll. A huge advantage of the vertical-scroll structure of all Spark Pages is that these pages are responsive, which means they will automatically adjust to look good on any screen: computer, tablet, or mobile device. Spark automatically generates a URL for each Page, which means that you do not have to worry about a host server for your Spark Pages, because Adobe servers handle that for you on-the-fly and in-the-cloud.
XD is a new generation Creative Cloud application whose primary purpose is to make it easy to design or "wireframe" the interfaces for mobile applications, which is where the name comes from, which stands for user-eXperience Design. XD makes it much easier for visual designers to build and prototype the look and functionality of a mobile application than using Photoshop or Illustrator to build such interfaces. However, the actual computer coding that runs the actual mobile applications is not part of XD -- that coding happens on the "back-end," with XD designing the "front-end" or user-experience interface. XD is thus extremely intuitive and easy for you to learn and use, because it emphasizes the look of the design, not the programming behind a mobile application. XD is a profound breakthrough for Adobe, and you can expect all of the other applications in Creative Cloud to become increasingly intuitive like XD. Because XD is so user-friendly and powerful, like all Creative Cloud applications, it can do much more than just design mobile apps. When you start a new project in XD, you can chose a "Web" project template instead of a mobile device template, and then you can leverage the power of XD to build simple and visually elegant websites. Be aware, however, that Dreamweaver is limitless in terms of its web-building powers, whereas XD is just an easy way to get started. You will need access to a web server to upload and share the websites you build in XD, and the application makes it easy for you to manage and upload those files.