how can I insert 4 excerpt's page inside a page?

you could use a page template:
http://codex.wordpress.org/Pages
http://codex.wordpress.org/Pages#Page_Templates

in the page template, before the loop, use:
query_posts
http://codex.wordpress.org/Function_Reference/query_posts
http://codex.wordpress.org/Function_Reference/query_posts#Post_.26_Page_Parameters
(important: use 'post_type' => 'page', apart of the parameters)

for instance:

$args = array(
'posts_per_page' => 4, // optional to overwrite the dashboard setting
'paged' => $paged,
'post_type' => 'page',
'post__in' => array(2,119,155,156)
);
query_posts($args); 	?>

(substitute the page IDs of your four pages)

if you need help with formatting, report back.