Not sure what you are meaning by 'using your own photos as Transitions'? Transitions determine how your pictures (or vid clips) change from one to another. Options such as twirl, wipe, and dissolve etc you just insert the effect you want inbetweeen each photo/vid clip. In Windows Movie Maker you Drag & drop it on to timeline or storyboard view. You can use both video transitions and video effects for your photos, there are different 'boxes' to drag them to in storyboard view.
OnePlus 5T review