There are a few things which need to be done to prepare for your own chosen eating plan. These will really help you to stay focused on what you're eating every day. You get to choose what you eat as long as it stays within the allowances which you need to create for yourself.
first of all you need to know how many calories, carbs, fats and protein are right for you. This is called knowing your macros. Don't be put off by this as it's all done for you here:
https://www.ruled.me/keto-calculator/
once you know your numbers, go to acaloriecounter.com, create an account and tap the "goals" tab. Type your numbers into the goals and save. You are now ready to add things to your diet for the day. Play with it to see how it works....everything you add is calculated for you and all you have to do is avoid going too much over your allowed amounts. Your carbs will be very limited as the aim of keto is to encourage the brain to use fats for fuel instead of glucose. This produces ketones in the brain which have been found to be beneficial to neurological conditions. Look up the research.
it will seem cumbersome to type in everything you eat every day BUT after a week, you can go back and repeat any day's food....in fact I got to know what to eat so well I abandoned the counter after a couple of weeks. You can create your own foods from supermarket labels if they're not on the counter's AMERICAN food list. That way they can be added to your day with just a tap.
i myself will be starting over, this time with hubby, in the next day or so. Yesterday I did his numbers for him....I have to wean him off toast and marmalade!
good luck.....anything else just ask.