Tools

Realistically speaking you shouldn't need to worry to much about food.
You eat natural foods, no sugars or processed carbohydrates. And that alone should be enough. At least for many people.
It is easy to imagine a time we, as a species, did just that.
Unless you're doing Keto for health reasons, like cancer, diabetes, Alzheimer's, PCOS, epilepsy you will be ok to just keep a mental note of what you eat.

But sometimes you may want more, or quicker, or kickstart your weight loss.
Whatever the reason there are tools that you can use.

Macros

Most Keto websites will mention macros in one shape or another. Many will even provide Macro calculators.

Dr. Jeff Volek and Dr. Stephen Phinney certainly mentioned macros in their book. And the reason for it is that we, as a modern society, had deviated greatly in the last 200 years in comparison to the thousands and thousands of years before. When looking at societies where modern man had little to no impact, the difference between their diet and ours formed the basis of the macro calculations we use today.

So, although many experts will tell you don't have to calculate your macros, and they would be right, the reality is that for most of us our perception of portion needs adjustment. 
We shouldn't be aiming for 45% carbohydrates or more in our plates, and yet that is what the standard guidelines advises and all the food commercials, shopping aisles and most of your friends will make you believe. It is hard.

So as a tool, if you feel your energy levels are low and weight loss has slowed down, calculate your macros. Your calories should roughly come 5% from carbs, 70% from fat and 25% from protein. Tweak accordingly.

Keto Calculator  

Tracking

If just knowing your macros doesn't help then you may chose to track them.
You can either  

My Fitness Pal

Fasting

Supplements