Being able to "relate to" a feeling or experience means that you understand it. It might mean that you've had the same feeling or experience before. In other words, this is an expression for showing sympathy.
Most parents can relate to the feeling of being overwhelmed when you have your first child.
I've been made fun of my whole life. I don't know if that's something that you can relate to.
You usually talk about "relating to" a feeling. It's a little odd to directly say "I relate to you" though. Instead you might say something like:
I can relate to your situation.
I can relate to how you feel. The same thing happened to me when I first moved here.