Hi Karla,
Let's Encrypt is fully automated so there is no human being to submit the CSR to. Instead, you install special Let's Encrypt software somewhere (called a Let's Encrypt client) and that software can submit the CSR for you. Then either the software or the user has to make changes to the web sites mentioned in the CSR to prove that the user really controls them, and finally the client software will receive and save the certificates, which can then be imported into web server software.
There is a full list of available client software available at
If you're not prepared to install one of these on a computer, you can also use the web-based ones in that list, which involve interacting with a web site instead of installing a program.