使用SQL Server 2008中的值更新一个数据库中的记录?

I need to update my new database with data from 1 column in my old database. Basically based on matching ItemID's I need to set the Description column in my new DB with the values in the old DB. I can see what needs to be updated when I do a join but I am not sure how to handle this update properly. I need to update my new database with data from