Load Data (Book) To Text Box When User Just Enter The Book Code?

how to load data (Book) to text box when user just enter the book code?how to load data (student) to text box when user just enter the student id?how to write the code when user click the save button , the book quantity(Book) will reduce 1 and the all the data in textbox will save in database(Issue)the interface is like

[URL]

the database is show at

[URL]

the code is

Public Class frmIssue
Dim dt As New DataTable()
Dim rowIndex As Integer = 0
Dim rowIndex1 As Integer = 0

[code]....