Hello and welcome to slim fast. I'm sure you'll do super well if you can get on with it..... I personally love this diet!
For dinners there isn't too much advise I can give you with out going into whole recipe ideas... Don't think that's quite what you wanted. I know alot if people use ready meals as their main 600cal meal, purely for the fact it's easy (ie it's calories are already calculated) an just add a slice of bread, veg or a pudding to make up the calories. I personally like to make fresh stuff, but that's personal preference (as most of the time I'm cooking for myself I put left overs in the freezer, then I can just throw them in the microwave when I'm being lazy)
As for snacks.... These are the fun bit!!!! Allowing you not to feel to deprived!!!
Supermarkets do a while range of less the 100calorie cereal/chocolate bars and crisps.
Alit if the special k bars, mini toffee crisps, break aways etc and then there's crisps.... (multipacks of) French fries, squares, quavers, skips are all under 100cals.
For treats I use one of my 100calorie snacks for things like a gin and slimline tonic, or 2 Maryland cookies, or a cadburys highlight hot chocolate with 2 marshmallows in the top!!!
Plus theres always fruit.... You can have a surprising amount if fruit for a 100 calories, a banana, a bowl of strawberries and blueberries, several satsumers! I make sure I have at least 1 normally 2 of my daily snacks as fruit.
Good luck!