Here are the answers to your questions:
Question 1: Which definite article should you use for the word garçon?
Answer: le (because "garçon" is masculine)
Question 2: What does le professeur mean?
Answer: the teacher (male) (Note: "le professeur" can be gender-neutral in some contexts, but traditionally it is male)
Question 3: Which definite article should you use for the word étudiante?
Answer: la (because "étudiante" is feminine)
Question 4: When can you guess the gender of a noun by looking at it?
Answer: Some words have an extra ‘e’ at the end. (Feminine nouns often end in 'e')
Question 5: What does l’amie mean?
Answer: the friend (girl) (because "amie" is the feminine form)
Feel free to ask if you have more questions!