newbie: help with array

I have database table that contains userId and permissionId. I want to query this table and make an array/list of permissions for a user when they login and assign these to a session variable called $_SESSION["userPermissions"]. On other pages i want to check if their $_SESSION["userPermissions"] array contains certain permissions and only allow certian bits of code to be displayed if it does. I have the query to get the permissions from the database but after this im not sure what to do. Any help on how to do this would be much appreciated.