Question about lexicon lambda

Hi, it’s not exactly a question about a steinberg product, but I couldn’t find the answer or another place to ask it.

I am using Lexicon lambda recording device. I manage to input microphone and instrument but I can’t get input from the computer, I want to be able to insert a device like headphones to the lambda and to be able to hear what the computer play (like in youtube for example). and also maybe record those sounds.
Lambda sends output to the computer but doesn’t get input from it.
please help me!! I am hopeless.