Are you getting errors referring to parameters? What's your code, failing, if so?
If it's just a general question:
A Parameter has two sides: If you develop a function you define parameters, to which values can be passed in by a caller. Parameters are simply variables, which are initialised by values calling code sends in. If you are the called, parameters are there for you to specify needed input, eg calling a file opening function you need to specify the file name you want to open.
Parameters make code flexible, something is done depending on the parameter values given.
Parameters can be optional or non optional, for example the DATE() function works without parameters, giving today's date, or with parameters, specifying any other date's year, month and day:
? DATE()
? DATE(2000,3,4)
On top of that you should watch some basic learning videos, eg
Even the VFP help has very good topics for learning language/programming concepts.
Bye, Olaf.