How do you use Func<> and Action<> when designing applications?

Question

All the examples I can find about Func<> and Action<> are simple as in the one below where you see how they technically work but I would like

Answer 1

Actually, i found this at stackoverflow (at least - the idea):

public static T Get  
    (string cacheKey, HttpContextBase context, Func getItemCallback)
            where T : class
{
    T item = Get(cacheKey, context);
    if (item == null) {
        item = getItemCallback();
        context.Cache.Insert(cacheKey, item);
    }

    return item;
}