The specific instructions for what you are looking for are in here:
https://support.google.com/docs/answer/3093281
Remember your Google Spreadsheets Formulas might use semicolon (;) instead of comma (,) depending on Regional Settings.
Once made the replacement on some examples would look like this:
=GoogleFinance("CURRENCY:USDEUR")
=INDEX(GoogleFinance("USDEUR","price",today()-30,TODAY()),2,2)
=SPARKLINE(GoogleFinance("USDEUR","price",today()-30,today()))
Those 3 cells would result in something like this (the second line prints the value 30 days ago):