Can you tell us what is a exact functionality you want on click of these buttons. Coz these buttons will have diff functionality in diff scenario;
Actually we used Next Button to dispaly next record from database; like suppose we have dispalyed 1st record on the form next button will display 2nd record and so on......
For that we just have to take all the records into dataset , take one global variable which will tell you the number of current record dispalyed. Then you just have to add one to display new record.
Also you can use next button to go on next page when we have dispalyed data in datalist.
see this link;
Same is with the previous button, we can go to previous record or page by using previous button.
And preview button we normally used in screen saver, when we are dealing with images.
We use preview button to preview the image in this case. see this link;