There may be more than one way to do it, or it may not be done at all. From your description, I assume the drain line is horizontal to the sink. If it is a 2" i.d. pipe, then you can either use a 2" x 1 1/2" X 1 1/2" "double elbow", or you can add another tee. If it is 1 1/2" i.d., you cannot connect two sinks to it.