Learn the words, then the commands
Free courses on SSH, hashes, JWT, DNS and LLM APIs. Each lesson goes from the definition to real commands and ends with exercises that check your answers.
Courses
Pick one. Lessons build on each other inside a course.
- SSH from zero
Connect to remote machines securely, use keys instead of passwords, copy files, open tunnels and harden a server.
Beginner 6 lessons, 60 min
Open course → - Hashes and passwords
What a hash is, how it differs from encryption, how passwords should be stored and how to verify a download.
Beginner 4 lessons, 36 min
Open course → - JWT explained
What a JSON Web Token is, how it is built, how signatures work and the mistakes that cause security bugs.
Intermediate 3 lessons, 28 min
Open course → - DNS from zero
How names become addresses, what each record type does, why changes take time and how to query DNS yourself.
Beginner 4 lessons, 42 min
Open course → - LLM APIs without the jargon
What a large language model is, how tokens and context windows work and how to estimate what an API will cost you.
Beginner 4 lessons, 40 min
Open course →
How a lesson works
- Learn: a plain-English explanation with real examples.
- Try: links to a free tool so you can see the idea working.
- Practice: questions and commands that check your answers instantly.
Jargon, explained
Short definitions with links to the lessons.