1 : Function or Method(s) Should be have Public Static
2 : then Go the form you want to access this Method;
3 : then Access by FormName.MethodeName;
The Name of Web form in Method or Function Assume is Registration;
Assume The Method or Function Name is EmpRegistration;
Go to the Form and Calling Place you want to Access the Method or Function
Then Type Registration.EmpRegistration (in Calling Place)
Then Simple You can access Your Function or Method.
I Hope This will Help you.