Creating variables: app or home?

[slysalamander]

Hello

I dont know much what are the differences between creating a variable in home or app.
The problem that I am having is that sometimes I do some operations in CAS and it automatically replaces the variables with numbers. Since im using a lot of different formulas with the same variables, most of the time it makes a mess if the variable is 1 or 0.
I would like to avoid this, because when i use CAS, i normally like to see the final formula first to check and only then substitute the values.
I was thinking about creating one program "solver blank" to arrive to the final formulas. And another program with the variables to substitute.
In order to do this i need to choose to create the variables in "app"?
What does it mean to create in "home"?

Another last question: how do you erase the variable value if you choose to create it in "app"?

Thanks for the help