Can someone please explain the rules about freezing, re-heating and refrigerating?

I am really confused about the safety rules about freezing, reheating, refrigerating, etc. If you can't re-freeze anything that's been defrosted and heated, can you not defrost some chicken , make a curry and freeze it, then heat it again to eat for example? Also, I was going to make a lasagne last night using some fresh pasta and then freeze it, but the lasagne packet said 'do not reheat' so I didn't freeze it as I umed I wouldn't be able to reheat it again once I'd defrosted it, but I'm sure mum cooks her lasagne and freezes it. Another thing is, when is it safe to put heated food in the fridge - do you have to let it cool completely at room temperature first? I am totally confused and I would really like to have this made clear to me, particularly as I want to cook more meals ahead for me and my husband, and I am starting to wean my baby and will be making batches of food to freeze and have ready and stored. If anyone can help, I'd love to hear your guidelines!