Matt Tennessen changed their profile photo
I'm guessing the video you watched had either a wooden or prefabricated metal corner bracket. Those typically work on knockdown tables by using the bolt to pull the leg towards the bracket, thus bracing it tightly against the walls of he apron. A substantial mortise and tenon would be my preferred method but depending upon your skill set or available tools that might not be a possibility. This Youtube video might be helpful for you. PS, don't attach the legs into the table top, just the aprons.