SSH lets you log in to another machine from your phone and run commands there as if you were sitting in front of it. The key pair is the part to get right, because the two halves have very different jobs.
Each one is marked as you go, and the explanation arrives straight after, which is
the part worth reading.
4 questions, marked as you go.
Tasks
These need your own device. Run the command in Termux, then paste what it printed.
The marking looks at what the output means, so spacing, version numbers and
ordering do not matter. If you have not installed anything yet, the
lesson covers the setup.
Generate a key pair and read the public half
This creates an ed25519 key pair and then prints the public key, which is the half you copy to a server. It writes to a demonstration filename and creates the key without a passphrase, so it never stops to ask you anything. The lesson covers protecting a key with a passphrase, which is what you want for a key you actually use.
Run this in Termux
On your own device. Nothing on this page executes it. The command runs in
your terminal, and this box only reads what you paste back.
You should see the banner, a fingerprint line, the randomart block, and then a single line beginning ssh-ed25519. It is the last line that gets copied to a server.
a new ed25519 key pair was generated
a fingerprint is printed for the key
the public key is printed in the ssh-ed25519 format
the commands actually ran
What a good answer looks like
The banner Generating public/private ed25519 key pair, a line saying where each half was saved, then a line naming the fingerprint as SHA256: followed by a short string. After that comes the randomart block, and then the public key itself: one line beginning ssh-ed25519, a long block of characters, and the label you@phone. The label is only a comment, which is why it carries no secret, and the fingerprint is what an admin compares to check they are talking to the right machine. The private key sits beside the public one in the file with no .pub on the end, and that one never leaves the phone.
Marking your own work
Both halves of this are checked in your browser, with no server involved, so nothing
stops you from pasting output you did not run. The tasks are written so that the
easiest way to pass one is to actually do it and read the result, which is the whole
intention.