How does one start to track the meal they take.

It would help if you told us what platform you're using-- the website, iOS app, Android app?

But in general, you go to your food diary and click on "add food" below the meal you want to log. Since it sounds like you're just starting, you won't have any foods in your recent, frequent, or "your" foods list, so you'll have to type in a search term and look for it in the crowd-sourced database.

It helps to have a food scale, which is less prone to user error than eyeballing or volume measures (cups, tablespoons, liters). And even packaged food can vary from the amount listed on the label for a serving.

It's a good idea to check database entries against package labels for accuracy, and to check entries for nonpackaged/commodity foods against reliable database such as the usda in the US, or something similar in your own country, due to potential user error in creating the entry, the possibility the manufacturer has reformulated the product since the entry was created, the possibility the user in a different country or region with a different version of the product, etc.

I know it sounds complicated, but as you log things that you eat on a regular basis, they will be waiting for you next time you want to log them.