It really depends on what kind of technology your developers are building on. Are they building a website in HTML and CSS? A native mobile app for iOS or Android? A cross-platform mobile app using something like PhoneGap?
The process for building an app will vary a lot depending on the technology. Even the format a developer will need the images to be in can vary -- PNG vs. SVG vs. other formats like PDF.
If you're interested in making the leap from design to developing apps yourself, I'd suggest first picking just a single technology platform to focus on (HTML+CSS is probably the easiest to get started with) and then searching for books or tutorials online. If that's less your cup of tea, you may want to check out tools like Squarespace or Adobe Muse -- you can export images from Adobe XD and then arrange those assets into a customized website layout.
Hope that helps!
I think the best thing to do is to sit down with them and find the best solution that works for you and for them. The technology that the developer uses can have a big impact on what materials you can provide them to complete the project. For instance, if you are using a component framework the way graphics are created and applied to components like buttons and UI controls varies greatly across formats.
So I would suggest setting up some time and walking through what you have and the ways that you can output your work and find something that works for both of you. There might be a few little tweaks that you can do that can make your developer partner's work a lot easier, making your project more successful.