まかない, 賄い in Kanji, is a meal before you start to work. You may get まかない if you work at a restaurant or diner in the afternoon or evening.
They don’t have to give まかない to you, it is up to them, but they should give you まかない if they said they would when they hire you. It can be free, half price etc. It is also up to them.
Read a recruitment ad carefully and find the word まかない or 賄い if you want to be fed at where you work.
The photo below is a seafood bowl as a まかない at a restaurant in Tsukiji Tokyo where you have a famous Tsukiji Fish Market. A seafood bowl is usually quite expensive so you are lucky if you could get one as a まかない.