Hi Dan! Yes your right, they mean the same depending on the usage. So basically "SA" & "NASA" is used to answer the question "SAAN" & "NASAAN" (WHERE?). "SAAN & "NASAAN" is used to ask about the location of someone or something or where an action took/will take place. But like other languages "SA" & NASA" are also used for any other purposes other than answering a question "WHERE". As what I have said earlier, it's usage depends on the situation but most of the time it is used to answer the question "WHERE". Example: Q: Nasaan ang salamin ko? (Where is my eye glasses?) A: Nasa loob ng bag mo. (Inside your bag.) Q: Saan mo nilagay ang salamin ko? (Where did you put my eye glasses?) A: Sa loob ng bag mo. (Inside your bag.) Ex: 1. Ang cake na ito ay para sa lahat. ( This cake is for everybody.) 2. Sa akin ang bag na ito. ( This bag is mine.) 3. Isa ka sa pina kamagaling na guro. ( You are one of the best teacher.) 4. Sa mga kamay mo nakasalalay ang iyong tagumpay. ( Your success lies in your hand.) Note: "SA" & "NASA" can be used in the beginning of the sentence. I hope this will help you. Enjoy learning "TAGALOG"

"Nasa" is used to indicate that something is in/at/on/etc. somewhere. "Sa" is used to indicate that something was done in/at/on/etc. somewhere or to someone. Other than this "sa" has like a hundred other functions, but those functions don't get confused with "nasa" so I'm not gonna explain them here. :p