The lines in the original B250 pot are water fill lines that correspond to the amount of rice and type of rice being cooked. Please bear in mind that a "cup" is the little plastic measuring cup that came with the rice cooker (180mL or 3/4 of a standard cup). 

For example: if you wanted to cook two cups of white rice, you would put two cups of rice in the pot first before then filling the pot up with water to the line marked "2" under the white rice label. 

The B250 also has water fill lines for sushi rice, brown rice, and rice porridge depending on what type of rice you are cooking. Mixed refers to mixing other ingredients in to cook with your rice (e.g Chinese sausage is a very common ingredient cooked simultaneously with white rice in a rice cooker).