Date Comparison Question

In my current job I am learning MS SQL - while having to write valid SQL statements. I need some help designing a query that checks hire dates for establishing participation for (something).

So the statement establishing participation has to have a WHERE clause that will check HIRE_DATE and establish two different goals:

1. WHERE Hire_Date < OCTOBER 1 of this current year
2. WHERE Hire_Date < OCTOBER 1 of previous year



Different question now that I am thinking about it: some of these previous SQL statements have a @ symbol, what does that mean in SQL? Can't find an online resource that references that symbol
Example: IF @Type IN ('Workflow','All')

Thanks for the help in advance.

Rob