.htaccess - htaccess convert request to clean url and add slash at the end of the url -

ok , searched more 4 days , more 20 posts here in stach or in websites without kind of success

first here htaccess file

rewriteengine on   rewriterule ^([a-za-z0-9_]+)/?$ index.php?page=$1 [nc]  rewriterule ^([a-za-z0-9_]+)\/([a-za-z0-9_]+)\/?$ index.php?page=$1&action=$2 [nc] 

i tried many codes 1 worked me can call request , works me

www.example.com/pagename => www.example.com/index.php?page=pagename

here questions , please provide me information "in detail" understand code well

1- how convert request automatically www.example.com/index.php?page=pagename www.example.com/pagename

2- if tried add slash @ end shows me page without images or styling mean www.example.com/pagename => works www.example.com/pagename/ => doesn't work

that's :)

for first part need 301 rule this:

rewritecond %{the_request} /index\.php\?page=([^\s&]+) [nc] rewriterule ^ /%1? [r=301,l] 

for second part use absolute path in css, js, images files rather relative one. means have make sure path of these files start either http:// or slash /.