How do you create this app? (water consumption)

Hi, I speak Portuguese, so sorry for the bad English!
I was trying to create an app where the user would enter their age, body weight and how many Ml's of water they consume per day. When the user clicked the "Calculate" button, it would appear how much water he should drink per day based on weight and age and it would also appear if he is drinking enough water based on the daily consumption entered by him. If the user drank more water than recommended, the Arduino would flash the green light, otherwise the red light.
How can I finish my program?
Idade = Age
Massa = weight
Ml's de água = Ml's of water
Consumo de água ideal = ideal water consumption
avaliação do consumo de água = assessment of water consumption
calcular = calculate