Nostr isn’t a specific client… Nostr (Notes and Other Services Transmitted by Relays) is what you do… Your NSEC is your key (do not share) that you use with any client you choose and your NPUB is your account associated in the client. There are several clients and even more relays. I use #Damus on my iPhone for my client and follow several relays.

https://nostr.com/get-started kinda covers the basics.

#Bitcoin is the Way!!! And we use #Lightning protocol to #Zap a note or image or npub we like.