How do I sell $100 in geezer language. I guess I’m computer illiterate

How do I sell $100 voucher in geezer language please. I’m computer illiterate.

Hi, welcome to the forum.
You can make a selling post in the marketplace saying what you have and what payment methods you will accept, you can also browse the buying section and see if anyone is looking for what you have available.
I would suggest you read the best practices too before you start.
Feel free to ask any questions if you are unsure.