ado connectivity

Foreign key (Let's say for Table_A) means primary key of another table (Let's say Table_B). So if Table_B has multiple rows then it will have multiple PK values, So, Table_A  FK column should have only those values which are present in Table_B primary key column.

So, when you insert a row in Table_B you can fetch the last PK value using Scope_Identity() and can insert it into FK column in Table_A.

using(SqlConnection con= new SqlConnection(cs))
{
SqlCommand cmd= new SqlCommand(@"Declare @FKId INT;Insert into Table_B(col2,col3) values (@param1,@param2);Select @FKId=Scope_Identity(); Insert into Table_A (col2,col3)values(@Param3,@param4)");
cmd.parameters.AddWithValue("@Param1",param1Value);
cmd.parameters.AddWithValue("@Param2",param2Value);
cmd.parameters.AddWithValue("@Param3",param3Value);
cmd.parameters.AddWithValue("@Param4",param4Value);
con.Open();
cmd.ExecuteNonQuery();
}

But, i will suggest you to use Stored procedure instead.