Eating during roza (fasting) is not permitted.
Now if someone eats by mistake then one should continue fasting. One should continue his/her roza as it is not broken.
Or if someone eats intentionally then one’s roza is broken. One should stop fasting and can eat rest of the day.
One should fast for whole day, before the twilight hour of morning till the twilight hour of evening.
Source Muslim sharif.
May Allah bless us and give us strenght to continue our roza and forgive us in this ramadan, month of purity.