powershell define starting point of script

I am fairly new to this but I am writing a script in PS, I have written all my functions (below eg) but how do I tell powershell to start with the 'menu' function which then links into all the other functions....

---

Function CreateFinanceUser
{
a load of commands specific to finance users
}

Function CreateAdminUser
{
a load of commands specific to admin users
}

Function Menu
{
a menu with choice to either create a finance or admin user
}