no, only in child tables
for the time being, don't bother with this part, leave it out and let it use the defaults
if you are just learning, the main thing is to see how a foreign key works "out of the box"
for example, if a parent row has one or more child rows, and you try to delete the parent row, what normally happens is that it won't let you do that, because the child row would then be an orphan, its foreign key to the parent row would be invalid
this is called relational integrity
there are options to override the "out of the box" behaviour, but you don't need to learn them yet