Process in installing a TV
The bracket should be screwed into at least one stud and preferably two. Drywall just doesn't provide the support for a large TV.
In the video, the center holes were screwed into the stud and the two end toggle bolts went in the drywall.
The bolt sizes will depend on the bracket you buy. In many instances, the bolts and screws will be provided. If they are not, the instructions will specify what you need.
There isn't really a good way to check behind  walls without a stud finder. You can push a long finishing nail into the drywall a number of times to determine the stud locations and move the nail around in the holes to &quot;see&quot; if you feel any wires or pipes. Since you're a homeowner, you'll be doing a lot of picture hanging,etc. so you'd be smart to get a good stud finder.