Drupal form submission - drupal

Question

I have created a form in drupal. I don't know how to handle the submission. I want to do some selection from database with the values i get from form. Here is my code to create form
function q_search_form() {
$form['qsearch']['category'] = array(
'#type' => 'select',
'#options' => array(0 => 'Any', 1 => 'Automotive', 2 => 'Real Estate'),
'#attributes' => array('class' => 'drop-box'),
'#prefix' => '<table width="470"><tr><td width="170">Select Category</td><td width="300">',
'#suffix' => '</td></tr>'
);
$form['qsearch']['city'] = array(
'#type' => 'select',
'#options' => array(0 => 'Any', 1 => 'Calicut', 2 => 'Kochi'),
'#attributes' => array('class' => 'drop-box'),
'#prefix' => '<tr><td width="170">City</td><td width="300">',
'#suffix' => '</td></tr>'
);
$form['qsearch']['property'] = array(
'#type' => 'select',
'#options' => array(0 => 'Any', 1 => 'House', 2 => 'Land'),
'#attributes' => array('class' => 'drop-box'),
'#prefix' => '<tr><td width="170">Property</td><td width="300">',
'#suffix' => '</td></tr>'
);
$form['qsearch']['wanto'] = array(
'#type' => 'select',
'#options' => array(0 => 'Any', 1 => 'Sell', 2 => 'Buy'),
'#attributes' => array('class' => 'drop-box'),
'#prefix' => '<tr><td width="170">Want to</td><td width="300">',
'#suffix' => '</td></tr>'
);
$form['qsearch']['submit'] = array(
'#type' => 'submit',
'#value' => t('Search'),
'#attributes' => array('id' => 'Search', 'class' => 'srch-button'),
'#prefix' => '<tr><td><a class="adv-srch" href="#">Advance Search</a></td><td>',
'#suffix' => '</td></tr></table>'
);
return $form;
}

Answer 1

You can write following submit function,
function q_search_form_submit($form, &$form_state) {
// To get selected values from form
$values = $form_state['values'];
// do print_r($values); exit; to check the values
}

Answer 2

This is pretty simple. You just have to implement the form_submit function. From the function above, I assume the name of your module to be q_search. So, here is what the submit function would look like:
function q_search_form_submit($form, &$form_state) {
// you can get the values submitted by the users using
// `$form_state['values']`, and use the database functions
// to implement your logic.
}
If you also want to validate the user inputs before the actual submit, you should add a validation function which would look like:
function q_search_form_validate($form, &$form_state) {
// validate here
}
You can use form_set_error, in the validate function if the validation fails.

Answer 3

You can do pretty much anything you want in the form_submit function.
function q_search_form_submit($form, &$form_state) {
$category = $form_state['values']['category'];
$city = $form_state['values']['city'];
//etc..
//use these values to query your database tables
$query = db_select($category, 'c');
//narrow results to those only in the selected city:
$query->join($city, 'cy', 'c.city = cy.cid');
//narrow results further with more ->join statements
$results = $query
->fields('c', array(fields you want from the categories table))
//fields from other tables...
->execute();
//do whatever with the $results (print on a different page, print in a table, etc).