How do you call a function passing in a lambda expression?

If I had something like:

public void add(func<string, string> 
val)
{
     textval = val; // val should be hello
}

And I want to call this function

add((val) => "hello")

>Solution :

public void Add(Func<string, string> val)
{
    var textval = val(""); // textval should be hello
}