Hello,

However, this is not working here.

Can you be more specific about what's not working? If the tool failed, please feel free to report the bug using the "bug" icon.

How do I specify that the strands I am extracting are in the fasta file in my account in Galaxy?

GFF requires a strand column, and the tool will automatically use this data to extract sequence data.

Should I be using another tool, please?

This is the correct tool. Finally, questions about using Galaxy and its tools are best directed to the galaxy-user mailing list, so I've moved your question to that list. Best, J.