I learned "fica" with Pimsleur in the context of asking where various buildings were located.
"Onde fica o hotel?" "Fica aqui."
"Onde fica o restaurante?" "Fica lá."
I don't know whether that will help anyone else with understanding usage, but it helped me once I realized it was the same word.
Portuguese has two verbs for 'to be' - ser and estar. Each has a different meaning. Estar can be used to show location, ser cannot. But DL hasn't taught estar yet. So they used ficar, another verb that can be used for location. It would be helpful if they would explain these verbs and how to use them. But DL is not intended to be the only means people use to learn a language. It is intended to supplement languages courses, not to replace them.
For anyone coming through here late, "ficar" can be used for multiple things. It can mean stay as in "Por favor, fica aqui", can be is kept as used in the example, and it can also be used as a state of being, like "eu fico feliz". Personally, I don't fully understand its use as a state of being. I have Brazilian friends who I talk to all the time, and they have said it is used for immediate feelings. So imagine, its your birthday and I give you a present. Receiving the gift makes you fica feliz. if anything is wrong with that, and you speak Portuguese native or just know more than me, please reply :)
"The salt stays in the kitchen." A possibly related saying, "like putting salt in an open wound" which is very painful . In this context one might use "the salt stays in the kitchen" as a polite way to tell someone that their choice of words is hurtfull and not productive, so clean up your language, by keeping the salt in the kitchen and not in our conversation. In other words stop bitting me.