B1
used to introduce the first idea, reason, etc., in a series
Dictionary examples:
First, I'll become a millionaire. Then I'll figure out how money works! (0.0)
First, let's plan our vacation. To the moon, right? (0.0)
First, tie your shoelaces. Second, remember you're wearing sandals. Third, laugh at yourself! (0.0)
First, I want to thank my parents. (12.6)