No problem. Let's break things down and make the problem understandable. You want to create/burn a video DVD, ie., a DVD that you can stick into a DVD player and it will play like a commercially created DVD you can get at any store. You have created the content and now you need to make the physical DVD.
First, let's look at what makes a video DVD a video DVD. A video DVD has "rules" that allow a DVD player to recognize and use then content. The first rule: it MUST have a minimum of two folders - AUDIO_TS and VIDEO_TS. TS stands for "transport stream," which is like .MP4, .MKV, .JPG, etc. Second rule: all of the DVD menus, videos, etc. are inside the VIDEO_TS folder and NO file can be larger than 2Gb. There are many other rules, but those are the two important ones.
DVDStyler is an application that let you create a video DVD, complete with menus, titles, etc. A DVDStyler "project" is ONLY the information that DVDStyler uses to create your DVD. For instance, it knows what photos you want to use and where they are stored, but it doesn't keep a copy of those photos for itself. This conserves space, but can also create a problem if you accidentally delete a photo. DVDStyler takes that information and creates bunches of files the DVD player can use:

To create a physical DVD, you have two options: burn directly to disc (not recommended) or create an ISO file. An ISO file (very similar to Mac OS's DMG/IMG disc image files) is like a Polaroid snapshot of a disk that is kept as a single file. I can double-click on an ISO file and most computers will simply load it up like a CD/DVD. I can also use an ISO file to re-create a physical DVD. If you click on the red disc at the top of the app, it will bring up this box:

I used to burn directly to disc, but sometimes I would waste a disc, simply because I didn't properly proofread a menu title. Now, I create an ISO file of my DVD and save it to my desktop. Once it's created, I simply double-click the ISO and it loads like I had inserted a physical DVD into my computer. I toodle around and make sure everything is the way that I want it. If there are edits, I simply overwrite the ISO file until it is my perfection.
Now, I burn my first physical DVD copy; first, I reboot my Mac to ensure nothing extra is running and the system is clean/good to go. Then, I use the app BURN to burn all my DVDs, both data and video (https://burn-osx.sourceforge.io/Pages/English/home.html). A long time ago, I was taught that apps do one thing really good and everything else ok. For instance, DVDStyler is great to create DVD layouts, but it is really primitive when it comes to actually burning a disc. So, I create the ISO in DVDStyler, but burn it with Burn. Once the disc has been burned and tested, I either toss the ISO file or copy it onto my network server for posterity. I've made probably a dozen or so DVDs for clients and after trial and errors during the first two projects, I streamlined my process and now I can spend more time on the content, rather than the burning process. If you think you will EVER need to burn another copy, keep the ISO file. You can use burn to create an ISO from an existing non-commercial DVD, but it's not recommended (see "bit rot".
The only other advise I can give is to SAVE OFTEN and to keep all of the photos, movies, files, etc. inside a "project" folder. NEVER use originals (ALWAYS use a copy of the original for your project). USB memory sticks are so cheap that I have a small box of them just for these projects. And once I have my ISO and know I won't need to change it anymore, I just erase the USB stick and toss it back into the box.
Hope this helps!!