Subordination in grammar refers to the process by which we link two clauses inside a sentence making one dependent on the other. It's constructed by a main or independent clause, and a subordinated clause that is attached to it by an adverb or an adjective.
Here are a few examples:
"While Bobby was in school, his dad prepared lunch in the house" (adverbial subordinate clause)
"All the pets jumped around with joy when Bobby got back home" (adverbial subordinate clause)
"Bobby, who was the best student, always got to pick dessert" (adjectival subordinate clause)
"They lived in his grandma's house, which she had built with her own hands" (adjectival subordinate clause)
Hope this helps!