submit buttons aren't that special, they just send a name and value like anything else :
<input type="submit" name="fruit" value="apple">
<input type="submit" name="fruit" value="banana">
Clicking the first will produce $fruit = 'apple' and the second will create $fruit = 'banana' and check accordingly :
if ($fruit == 'apple') {
echo 'you clicked on apple button';
}