Hi Binni
It's really hard to say. If you're a few stone over a healthy BMI then possibly but it's a difficult diet to give guarantees on, especially not knowing where you started from.
If you're dieting right now - say on a VLCD then you'd be unlikely to have a big first week loss. If you're not dieting right now then the average first week loss varies between around 3-7lb, with some people losing a little more or less.
It's then quite common for loss to stall for a week in either the second or third week - but again that doesn't happen to everyone.
After the first week the average loss is around 2lb per week - again for some a little more, fir some a little less.
The average Atkins loss is 1/2 a stone a month after the first month. The first month is often more as people might lose half a stone in their first week - that's called water weight, it's the body releasing it's stores of glycogen, and happens on most diets in the first week - if you then go back to normal eating you'd put that weight back on.
So, some people definitely do lose a stone in the first 3 weeks. A lot don't quite. And bear in mind it won't all be fat you lose in the first week. None of this is intended to be discouraging - if you stick to the diet you'll lose. I've lost nearly 2 stone in 3 months and had one week off plan.
As for what to eat - you need to grab a copy of the Atkins book, but to get a basic idea go to the stickies section and read 'so you're thinking of starting atkins'.
Good luck!