Great questions. Depuis means, 'for', for example, 'depuis trois ans, means for three years. Puisque means, 'since'. For example, 'puisque le vingt septembre', means 'since september'. 'Pendant' means, 'during' or can be used to mean that something took place over a course of time. For example, 'pendant cinq jours', means, 'for five days' and il y a is used to mean there is or 'ago'. So if i say, 'il y a dix jours', that would mean 'ten days ago'. hope that answers your question. If you'd like to practice speaking, I'd be happy to help you develop a study plan. Feel free to look at my teaching profile and class offerings and send me a message if you think I can help you. Have a great day :)

If your class textbook is inadequate, consider the Grammaire Progressive du Français series by CLE international. The intermediate book covers this in unit 41.

"Laure a fait un stage au Mexique pendant six mois en 2004" = Laure did an internship in mexico for six months in 2004 Depuis plus de 10 ans, elle a le bac = for more than ten years, she has Bac Elle espère changer de travail dans peu de temps = she hopes to change job in a bit of time Elle a commencé travailler il y a plus de 10 ans = she started to work more than ten years ago Elle est guide depuis 2012 = she is a guide (or more in everyday english, she has been a guide) since 2012