What i mean is, whats the difference between saying 青く and 青い? I could have phrased the topic better but yeah. i dont know if thats the same thing as the difference between 強い and 強く, but if its the same, now theres another example.
It's the same, it's a form of the -i adjectives. It's used in several ways, but the most common one is when you want to connect it to a verb (in essence making it an adverb).
黒くなる - to become black 明るくする - to make (it) bright 早く走る - to run fast 遠く行く - to go far
Unrelated - is this valid Japanese? It's tempting to translate the phrase "my ____ is bad" directly from English, but I've never known if it's correct to do that here.