First you need to know the following. Germans use two ways to communicate, the informal and the formal. The informal is casual. The formal is a polite way to speak to people
The casual way to say "I love you" is "Ich liebe dich" in German. "Dich" means "you"This is the most common version to communicate to someone that you love them because most probably you are already friends, and you know each other.
If in a rare occasion, where you have been talking to someone in a polite way (such as at work) and you want to confess that you love them, you can say this:“Ich liebe Sie”The “Sie” stands for a polite version of “you”.