Need some advice on transportation

I am a student planning a trip to Amsterdam, I found an Airbnb in Purmerend and because I won't be bothered to be 30 minutes away from Amsterdam, I think that it is the most suitable for my budget.

However, I don't have too many ideas about what is best for me concerning transportation fares. I need help with the following :

- How do I minimize the fares of going between Purmerend and Amsterdam on a daily basis ?

- What is the best option for me for transport within Amsterdam ? (I will be there for 5 days)

Any advice and help is very much appreciated. I am very new to this. Thank you.