If you are using dry malt it works better if it is added to cold water and then is brought to a boil. If it is added to boiling water it will tend to clump up and be difficult to work with. If you are adding corn sugar add that too now. Bittering hops are necessary if you are using unhopped malt extract. They can improve the character of hopped extract and kits as well and need to boil for a long time in order to reap their full benefits.
Hops act as a flavoring agent, as well as, aid in beer-foam head retention.
They too should also be added now. THE WORT Stir well until the extract is thoroughly dissolved. You should now boil your wort for one hour, although this is not strictly necessary when using hopped extract or a extract kit, it will help to stabilize the flavor of your beer. A good rolling boil is considered ideal, but you must watch your brewpot carefully to prevent a boil over, as this can seriously affect the quality of your final brew, not to mention making a sticky mess on the top of your stove. Some brewers will add additional hops during the boil, particularly if they are making a hoppy brew.