Can't change the pitch

This is about Audacity 2.1.3 installed on OS X 10.11.6.

I’m trying to change the pitch as shown here.

Under Effects, Change pitch is greyed out, like all but a few. It is, however, enabled under Effects>Add/Remove plug in.

What should I do?

Thanks.

All those effects are greyed out because you need to select some audio first.

– Bill