Carbohydrates are one of the dietary macronutrients, along with protein, fat and water. Carbohydrates (carbs) are necessary for good health, but you should minimize refined carbohydrates such as white flour and sugar. Animal products, aside from dairy, do not have any carbohydrates. Most vegetable foods are a mixture of macronutrients. There is no absolute definition of "low carb", and there are tens of thousands of food items to consider. There are lists of low carbohydrate foods available, but you should read them considering that "low" is relative.
Enter "low carbohydrate foods" into a search engine. There are a number of sites that give lists of low carbohydrate foods or tables where you can look up the foods. Two are given in the references.
For a book on the subject, enter "low carb food list" in the search function at Amazon.com, or ask at your local library or book store.
Go through the lists and note foods of interest to you. Many foods in these comprehensive lists will not be foods you want to eat, so make your own list that you can use to find low carbohydrate foods that you like.
Add to your list the pre-packaged foods that you enjoy. Read the label to find the carbohydrate content.
Add information on restaurant food you often eat. Most chain restaurants have nutrition information on their Web sites. Other restaurants will probably give you ingredient lists from which you can estimate the carbohydrate content of the meal.