To begin with just eat the following:-
Any kind of meat you like in it's natural form (not processed). With fat on it. Example: whole chicken, chicken breasts/legs, steak, pork chops, lamb, bacon (be careful with sausage, count carbs).
Eggs - however you like them but don't use sauces, cook in butter/lard.
Green leafy vegetables - try to have some with every meal, or at least 2 out of 3 meals. NO carrots, corn or potatoes, think more like cabbage, spinach, anything green to be safe.
That's it really. There are other bits you can add in too which make it more interesting which you can learn as you go along, but to get started immediately the above will help. Here are some other things you can have:
cream (limited amounts)
cheese (check carb count, cheddar is OK, also a small amount of soft cheese)
mayonnaise (check carbs and don't get the low fat stuff!)
fats - whole, natural fats are better than processed stuff, go for olive oil and lard.
sweeteners - be careful and limit as much as possible
drinks - water or tea/coffee, not meant to have milk but i know some here do, if you do make sure you count the carbs. Try cream instead of milk as its lower carb.
pork scratchings/pork crunch - check the packets for carb counts ,some have a lot of rusk in them, the ones i get are around 0.3 g / pack so fine.
Count any carbs and make sure you don't go above 20g for your first two weeks. Vegetables have carbs but green leafy ones have the lowest amount. Ideally you are meant to have 15g of your carb allowance dedicated to veg, and the other 5g to other things (eg cream, pork scratchings, etc).
There is a sticky at the top of the forum which goes into more detail on how to do Atkins and what you can eat.