About how I do these, first the backgrounds:
I usually get the background images from existing videos. I watch the video in full screen, stop it at the point I want to capture and make a screenshot, saving it as 1920*1080 PNG image.
If it needs editing I do it in the Windows Paint. In the case of the image in my previous post, I used PhotoShop to create the lighter one from the darker original.
For text slides inserted in videos, I use PowerPoint. You don't have to use the paid for version, the free PowerPoint Online and / or PowerPoint Windows App available from Store (Beta) are enough.
I use these Ten Forums themed backgrounds as the slide background in PowerPoint, usually the darker one in the title slide where's less text, and then later the lighter one with the explaining slides with more text so that the text is better visible.
When I am done with the PowerPoint presentation, when I have created all the slides I need, I start a slideshow in full screen. Now I create a full screen screenshot of the slide 1, then move to slide 2 and do the same, and so on. This results a bunch of image files, each showing one slide intended to be inserted to the video, which I can then import to Movie Maker and place where I want them.
That's something to start with .