Accounts on crates.io are created by logging in with GitHub; you cannot sign up with any other method.
To connect your GitHub account to crates.io, click the 'Login with GitHub' button in the top menu bar and authorise crates.io to access your account. This will then log you in to crates.io, assuming everything went well.
You must then find your API key, which can be found by clicking on your avatar, going to 'Account Settings' and copying the line that looks like this:
cargo login abcdefghijklmnopqrstuvwxyz1234567890rust
This should be pasted in your terminal/command line, and should authenticate you with your local
Be careful with your API key - it must be kept secret, like a password, otherwise your crates could be hijacked!