A newline can be included in a single-string or double-quoted string. Note that backslash-newline does not result in a newline, the line break is ignored.

newline1='
'
newline2="
"
newline3=$'\\n'
empty=\\

echo "Line${newline1}break"
echo "Line${newline2}break"
echo "Line${newline3}break"
echo "No line break${empty} here"

Inside dollar-quote strings, backslash-letter or backslash-octal can be used to insert control characters, like in many other programming languages.

echo $'Tab: [\\t]'
echo $'Tab again: [\\009]'
echo $'Form feed: [\\f]'
echo $'Line\\nbreak'