To add simple filters on your search query with apachesolr can be easily done through hook_apachesolr_query_alter. You'll find the documentation on path/to/apachesolr/apachesolr.api.php. An example would be:

<?php
function module_apachesolr_query_alter($query) {
  $query->addFilter('bundle', 'page');

  // To filter by either page or article content type
  $query->addFilter('bundle', 'page OR article');
}

For adding subqueries (which is a bit different), you may do this:

<?php
function module_apachesolr_query_alter($query) {
  $sometid = 1;
  $filter = new SolrFilterSubQuery('AND');
  $filter->addFilter('bundle', 'video');
  $filter->addFilter('tid', $sometid);

  $compiled_filter = new SolrFilterSubQuery('OR');
  $compiled_filter->addFilter('bundle', 'faq');
  $compiled_filter->addFilterSubQuery($filter);

  $query->addFilterSubQuery($compiled_filter);
}

In here, I've used addFilterSubQuery for the final query as when you do $query->addFilter('bundle', 'faq'); $query->addFilterSubQuery($filter), the operator would be AND. For filtering, you can go to admin/reports/apachesolr to find the available fields.

Cheers! :D