How Can I Passing Foriegn Key Value To Datagridview That Is Build By Bindingsource

hello
i am new programming in vb.net , so i have 3 tables it is linked to gather by many to many created it in sql server database

<big style="margin:0px;padding:0px;border:0px;">first table Trainingtable </big>
train_id [primary key][Auto number]
train_name

<big style="margin:0px;padding:0px;border:0px;">second table Employee table </big>

empl_id [primary key]
empl_name


<big style="margin:0px;padding:0px;border:0px;">Third Table train_empl</big>

train_empl_id [PK]
empl_id [foriegn key]
train_id [Foriegn key]
mark

so i am  entering data of training data table by text boxes and 
the train_empl table data entering by datagridview and the employee table data entering by combobox it is inside datagridview


i am getting its value and saved it in variable but i am not know how can i insert it to its table(train_empl)

i am using binding source to link datagridview (train_empl Table) and its Combobox (employee_Table)

my question How can i passes the value of train_id to datagridview?