I've alternated between very low carb and keto for a good few years. I started with low carb about 10 years ago and lost 1.5 stone in 3 months, and have learnt a lot about the science behind it. I've also learned that when I eat what is considered a normal amount of carbs, I don't feel well. I have far more energy without them.
Keto is very low carb...usually 20 to 50 grams of carbs per day for weight loss. That means no bread, rice, pasta, cakes and other sweet foods. Fruit is also limited...natures candy as some might call it. Plenty of green leafy veg, berries, meat, fish, poultry, eggs, dairy...in other words...real unprocessed food. Some good fats...olive oil, butter, coconut oil, avocado, fatty fish like salmon or tuna. Buy what you can afford...it doesn't have to be grass-fed. Also, don't believe the hype about eating loads of fat...that's not true. Particularly for weight loss. ;)
Take a look at The Diet Doctor website...plenty of good advice, recipes, and science.
If you've come from eating a rubbish diet, expect the Keto Flu...feeling somewhat rubbish for a while. Often due to withdrawal from over salted foods. Add some lo salt to a bottle of water for missing electrolytes.
There are some knowledgeable writers about so you can read about it if you want. Gary Taubes comes to mind.