The official documentation has instructions that work on most UNIX-based operating systems.
If you’re on Windows, you might want to look at alternative clients that have better support for that OS.
If you’re not familiar with the command line, SSL or web hosting in general, maybe a web hosting provider that includes support for Let’s Encrypt would be a better option for you. There’s a community-maintained list available here.
It would be useful to include more details about your environment (Server OS, Hoster, etc.) so that we can give you a more specific answers.