Frequency is how often you practice (interval). The more often you practice, the better. For example, if you only practice a skill once a week, you will see very little progress. For learning a language, you should practice at least twice a day, everyday. For example, you could pratice during class and at home (homework) or during tutoring in the morning.
Duration is how long you practice at each interval. Practicing for five minutes does little to improve your language learning. Practice for as long as you can, but at least
Length of time is how long you study. In language, we typically measure this is years.
Don't forget about summers or other school vacations. If you don't practice during these times, you're skills will get worse.
Quality has to do with the intention and effort you put in. If you sit at a piano and just bang the keys, you'll never learn to play. The same thing goes for learning a language. You need to focus and do your best to understand and respond.