How do I log food or a meal?

Tap "Overview", then the "+" on the "Log a symptom or a reading" card, and tap "Food". Search for the food, tap "Scan" to scan a barcode, tap "Camera" to use a photo of your meal, or pick from "Favorite" or "Recent"; if a search doesn't find it, choose "Enter manually". You can also type what you ate into the "Log a symptom or a reading" field.