An introductory clause is typically placed at the beginning of a sentence. It sets the stage for the main clause that follows. For example:
"Although it was raining, we decided to go for a hike."
In this sentence, "Although it was raining" is the introductory clause, and it comes before the main clause "we decided to go for a hike."
Introductory clauses can also be placed after the main clause, but when they do so, a comma is usually not necessary. For example:
"We decided to go for a hike although it was raining."
In this case, "although it was raining" is still an introductory clause but follows the main clause.