How do I enable the dictation facility on my Mac (late 2015

Thank you Luis Sequeira1

Are you able to expand on this for me?

1. I wish to be able to transcribe speech to text via my Mac.
2. I don't have an Fn key on my keyboard.

I would really appreciate it if you could help me understand this process. I am an old bloke who is not very good with technology. It would benefit me greatly due to hearing problems.

Thank you very much

Bob