INSERTing a student info record based on form inputs
Like I had mentioned in my comment this is vulnerable to sql injection. Assume the user of your application inserts Robert'; DROP TABLE StudentInfo;-- that would result in a query text of "insert into StudentInfo values ('Robert','',''); DROP TABLE StudentInfo;-- ', 'theName', 'theComboboxValue') " resulting in deleting your database table StudentInfo which isn't what you want !  

The solution to this is using SqlParameter's which will escape the provided values in a way that this can't happen like so  

string query = "insert into StudentInfo values (@first, @second, @third)";
SqlCommand command = new SqlCommand(query, cn);
command.Parameters.AddWithValue("@first", textBox1.Text.Trim());
command.Parameters.AddWithValue("@second", Name.Trim());
command.Parameters.AddWithValue("@third", comboBox1.SelectedItem.ToString());
command.ExecuteNonQuery();


I have named the parameters first, second and third, because I don't know what their meaning is, so you should give them proper names yourself. The @ needs to be at the beginning so that the names can be parsed to the desired parameters.    

Naming is very important in programming, so you should always use proper names for anything you do. If you come back in 2 weeks to this piece of code you won't know for what e.g textBox1 or comboBox1 are standing.