(1) "The squirrels hid the nuts at their usual place where no one would find them".
(2) "The squirrels hid their nuts, which they had carefully gathered, at their usual place".
(3) "Having spent all autumn climbing trees in search of food, the squirrels hit their nuts at their usual place".
Those are all examples complex sentences, the type that contain a subordinate clause. The underlined subordinate clauses in (1) and (2) are relative clauses, and in (3) it is an adjunct (adverbial).
