Since you are here, you have a key pair: a public key (npub) and a private key (nsec). You can log in to a Nostr client with both. Even with a public key. With any public key. If you take, for example, a stranger's public key, you will see that person's timeline. However, you cannot post new content with it. To post content, you need the private key.
It's best not to enter your private key directly into a Nostr client, as that would not be the safest way. While most developers are reputable and would never do this, and most Nostr applications are open-source anyway, it could still happen that - especially with newer, unknown or closed-source applications - someone might simply save your private key that you entered for login somewhere. With that, they could collect a few private keys and log in and post in your name. Your private key would then be compromised, and you could forget about it.
To keep your private key always secure, it should never leave your local computer environment. For this, there are so-called 'seed signers'. They ensure that your private key is never transmitted to the application, but they still manage your login to a Nostr client.
The most popular seed signers are probably Alby (https://getalby.com/) and Nos2x (https://chromewebstore.google.com/detail/nos2x/kpgefcfmnafjgpblomihpgmejjdanjjp and https://addons.mozilla.org/en-US/firefox/addon/nos2x-fox/) as browser extensions on the web.
Others are Keys Band (https://keys.band/), Nostrame (https://chromewebstore.google.com/detail/nostrame/phfdiknibomfgpefcicfckkklimoniej) and Nostr Connect (https://chromewebstore.google.com/detail/nostr-connect/ampjiinddmggbhpebhaegmjkbbeofoaj) for Chrome-based browsers.
For Android apps, there are Nsec.app (https://nsec.app/) and Amber (https://github.com/greenart7c3/Amber/releases) which can also be obtained via the Zap Store, Obtanium or f-droid.
A small side note: The Zap Store is particularly cool because you can also zap the developers and support them directly.
However, not every Android app yet supports an external seed signer, but that's just a matter of time.
What I also want to mention here for beginners is, never use a Nostr client without a VPN. As soon as you post, like or otherwise interact, your current IP address is also transmitted to the relays.
#nostrecosystem
quoting nevent1q…g67mAfter so many new Nostriches have escaped the "free speech" illusion of the fiat social media and found a new home here, we should properly onboard them and show them a bit of what has happened in the first 2 years. Because an account and a Lightning Wallet is not everything.
They say that zapping is the innovation of Nostr. That's true, but it's not the only one. The key pair with which we log in here also plays an equally important role. Because it fulfills the purpose of "one key - multiple apps". Similar to how you can log into multiple Google apps with a Google account, you can also log into multiple Nostr applications with your Nostr key. And there are many of them by now.
So in the near future I will introduce some of them and show what else you can do with your key. #nostrecosystem