Regarding Update In Asp.net Application

i created a asp.net application using sql server. it retrieve data from a sql server and shows it in the form. it uses textbox control
to show it. i wanna update it or add a new item in database. i wrote the code for it under update and add buttons.
when i click on the update button after changing a data in textbox, the page is getting refreshed nad comign back to initial state without getting updated. but when i change the textbox1.text with a string in the code, its getting updated with string without any problem. even same problem for addition too, am using a dataadapeter and dataset for this. when i assign a string to the datset columns, its getting updated well but when
i assign it with textbox.text.tostring, nothing is happenig to database. can anyone help me in this issue, why the data was not sent to the datbase and the page is getting refreshed.. plz need help.. its urgent