Navigate to Settings>Apps>Startup
Find the program you are wanting to add/remove from startup and turn it on/off.
To add a program or file that is not listed in the startup apps list, hit Windows+R to open the run menu. Then Run "shell:startup"
This opens up a File Explorer window for the path C:\Users\[CURRENT USER]\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup
Any shortcuts you place in this folder will open on startup. This can be useful for signage as you can place a ,ppsx file here and it will autoplay on startup.
To remove apps and files from shell:startup simple delete or move the shortcut.