Most restaurants do not lose money because the food is wrong. They lose it in the twenty minutes between a guest sitting down and the order reaching the kitchen, in the table that stays dirty for a quarter of an hour after it clears, and in the dish that goes out remade because a handwritten ticket was misread.
Operations is the work of removing those gaps one at a time. That means knowing your actual table turnover time rather than guessing at it, having a kitchen process that survives a rush without shouting, and writing down the opening and closing routines so a shift does not depend on whichever senior person happened to turn up.
The guides below cover each of those in order — measure what a service currently does, fix the step that costs the most, then make the fix permanent with a checklist. Start with the operations guide if you want the whole picture, or go straight to table turnover if your problem is that a full restaurant still is not making its numbers.