when you create a table, the default is "ON PRIMARY" for it unless you specify something else. To direct it to your 2nd file group specify "create table ... on secondary" or whatever name you called it.
from BOL:
How to place an existing table on a different filegroup (Enterprise Manager)
To place an existing table on a different filegroup
Expand a server group, and then expand a server.
Expand Databases, expand the database in which the table belongs, and then click Tables.
In the details pane, right-click the table, and then click Design Table.
Right-click any column, and then click Properties.
On the Tables tab, in the Table Filegroup list, select the filegroup on which to place the table.
Optionally, in the Text Filegroup list, select a filegroup on which to place any text, image, and ntext columns.
to see where it's defined use SP_HELP tablename and it will show where the table is located.