Duolingo is a good way to learn or brush up on basic technical skills, but not so much use in everyday conversation. Duolingo starts with basic vocabulary and some verbs. It teaches translations and conjugation, but not what you’d find in conversation or anything about culture. While it does give a good foundation that you could use in relation to things like textbook material and ‘set phrases’ such as asking for the bathroom, it’s not recommended if you want to hold an actual conversation with someone or learn the ‘flexing phrases’ what you need to ‘survive’, such as ordering various things in a restaurant. What it teaches could certainly help in reading/writing, but wouldn’t dramatically raise your literacy.