I have a recipe that I want to modify, but I'm not sure how to. Cooking is not my forte.

So, here's the list.
I want to substitute agave nectar for the sugar. Is there a coversion chart somewhere I can look at? And would I need to add extra volume, like I do when substituting stevia for sugar?
I have some organic yogurt that says it can be substituted for cream. The recipe calls for heavy cream. Can I use the yogurt? If so, how do I use it? The cream has to be brought to a boil. Not sure you can boil yogurt.
Also, how the heck do you scorch sugar? I tried and it was NOT working.
Thanks!