You can always use plain old + or << to add a variable value into a string:

drink = "espresso"
"I love " + drink
# ==> I love espresso
"I love " << drink
# ==> I love espresso

But if you want to do it for non-string values, you have to use .to_s to make it a string:

age = 26
"I am " + age.to_s + " years old."
# ==> "I am 26 years old."
"I am " << age.to_s << " years old."
# ==> "I am 26 years old."

This is complicated, and complicated is not the Ruby way. A better way to do this is with string interpolation. The syntax looks like this:

"I love #{drink}."
# ==> I love espresso.
"I am #{age} years old."
# ==> I am 26 years old.

All you need to do is place the variable name inside #{} within a string!