Collin gave good examples but you have to learn the difference. I know it is mean. I wear your shoes right now. I know and understand you can struggle a little bit with that because I did too. The best tip I can give you is: try to guess with the meaning of the sentence. Most of the time I can know if it is an adjective or a noun.

Unless I misunderstand the question, the difference is simple. "Ambition" (ambizione) is a noun, meaning a "goal".. My ambition is to speak Italian.. "Ambitious" (ambizioso) is an adjective, meaning "wanting to get ahead" or "waiting to achieve a goal". He was ambitious at work, trying to get a promotion. Neither of these words has anything to do with past tense, as they are not verbs.

He is very ambitious He has a strong ambition