SQL & PL/SQL

I'm converting from SQL Server and am struggling with how to build and test a procedure. In SS I would declare the variables I would use as parameters, assign values and write the code for the query. All this would be done in Enterprise Manager. I need to do something similar in TOAD editor

Declare @ID int
Set @ID = 100
Select * from tablename where IDField = @ID

From this I could then asses the validity of the parameter used by inspecting the results in the grid. Is it possible to do the same in the TOAD editor (I know I can use a literal but I need to test the treatment of the variable).