The sentence, 'When my family went on vacation, we were able to see many new places' is a complex sentence.
Explanation:
The above mentioned sentence is structured in a complex way. Complex sentences are the ones which contains one independent clause and one dependent clause. When my family went on vacation, we were able to see many new places, here we can see that it contains a dependent clause 'When my family went on vacation' and one independent clause 'we were able to see many new places' making it a complex sentence. Both the clauses are being separated with a comma.
