OK. What I think you’re asking is, “if I declare a variable in my script, can the functions also in that script ‘see’ that variable?”
The answer is, “probably, and maybe,” but you may not understand about PowerShell scope. If you’d like to learn more about it, read about_scope in the shell’s help system.
However, AS A BEST PRACTICE, you SHOULD NOT do what you’re asking, whether the shell allows it or not. You SHOULD declare parameters for all of your functions. Functions should be entirely self-contained, meaning they get all of their input only from parameters, and they output only to the PowerShell pipeline. They don’t “share” variables. Doing so makes functions dependent on that particular script, which is a Very Bad Practice.
Just declare parameters for every function separately. It’s the right thing to do and will save you a lot of debugging time later on down the line.