How can I use the same random variable in the two page? [php] [closed]

I want to use the same radom variable (my key) and send it from first page to next page for example second.php.

The situation is that in my first page (log.php) after identification some client , my key is generated and i want to use this generated key in second.php page.

I tried session, include and i have problem all the time.

Please, Can You help me with that? :)