Multiple "Where" values in a query.

I need this query to select 2 different pieces of information from the database using a $_GET method. But how do I make it so that I can have more than one WHERE?

SELECT
				 f1.cat_id as CatID,
				 f1.cat_name as CatName,
				 f2.sub_id as SubID,
				 f2.sub_name as SubName

				 FROM

				 forum_cats as f1
				 	LEFT JOIN forum_sub as f2
				 		ON f1.cat_id = f2.cat_id

				 WHERE f1.cat_id = '$cat'

I need it to also do

WHERE f2.sub_id = '$sub'

I tried using the AND feature, but it doesn't work how I want it too.

Thanks in advance,

Andy.

Worked it out