You can do this on Shopstr.store or on Amethyst. I don't have a guide, but it's not overly complicated. On the web, sign in with your NIP-07 extension and tap the add new listing button. On Amethyst tap the price tag button on the new post bar.

nostr:npub14u43en9xrzh92lmy8yk6fq3mme7vyul7x66n2zl6y35c3nt3y0lqhs3g74 recorded a walkthrough of using nostr:npub15dc33fyg3cpd9r58vlqge2hh8dy6hkkrjxkhluv2xpyfreqkmsesesyv6e a while back; it’s a little outdated but the main functionality has stayed pretty much the same:

https://www.loom.com/share/f229bfe81d8a4c008f36d8cc51913c1f?sid=aa90d9aa-8aa0-45cc-8e72-40a88f95b675

Since then we’ve added listing edits and a way to change the Cashu mint that is being used. We’re planning on making and releasing a new demo video after we roll out a few more features that are currently underway.