You can also search https://www.google.com/search?q=bash and follow links to "Documentation"

    xargs echo <<EOL  
    > line 1
    > line 2  
    > EOL
    line 1 line 2

    $ cat <<EOL
    > line 1
    > line 2 
    > EOL
    line 1
    line 2

Doing this:

"cat << EOL

line one

line two

EOL"

Would be the same as this:

"cat < file"

That is if 'file' contained this:

"line one

line two"

This doesn't work with the echo command because it does not use stdin like cat does.