Dim vars As Variables
Dim variable As String = vars("VariableName").Value.ToString()
and then use your variable as you need.
To write to a SSIS Package variable in a Script task that you're working on, so future tasks in the package can use it, use the following
Dim writeVars As Variables
writeVars(0).Value = "Hello World"
If you're using a variable to hold a value established in a Script task for use in further tasks, make sure its scope is not limited to just the script task we've made here.