The words whenever and wherever are subordinating conjunctions. If you begin a sentence with whenever or wherever, you are writing a subordinate clause. You must add a comma and an independent clause to make a complete sentence.
Incomplete clauses with whenever:
Whenever I eat strawberries
Whenever it rains
Whenever the doorbell rings
We need to add a comma and an independent clause to make a complete sentence, like this:
Whenever I eat strawberries, my mouth gets itchy.
Whenever it rains, a puddle forms at the end of the driveway.
Whenever the doorbell rings, my dog starts barking.
Incomplete clauses with wherever:
Wherever I go
Wherever I hide that blanket
Wherever we decide to go for vacation
Once we add a comma and an independent clause, we get good complex sentences, like this:
Wherever I go, my cat always follows.
Wherever I hide that blanket, Sammy still finds it.
Wherever we decide to go for vacation, I hope it’s warm.
When you begin a sentence with the subordinate clause words whenever and wherever, you must add a comma and an independent clause to make a complete sentence. We call this a complex sentence.