Are you looking for the string contains a certain number of words or contains specific words? Your example leads towards the latter.
In that case, you may wish to look into parsing strings or at least use regex.
Learn regex - it will be useful 1000x over in programming. I cannot emphasize this too much. Using contains and if statements will turn into a mess very quickly.
If you are just trying to count words, then :
string d = "You hit someone for 50 damage";
string[] words = d.Split(' '); // Break up the string into words
Console.Write(words.Length);