It's just a matter of matching the phpbb style with the wordpress theme. I'm not aware of any style that would match with any of the wordpress themes. So you need to do the job yourself or hire someone to do it for you.
Are there any guides related to this? I searched but could not find anything good. But I remember seeing something like this before.
If that is a question about "crontab" then all i know about it is that it is a Linux file used to control the running of cron jobs - an answer that would have taken you all of five seconds to search for.
Either someone misunderstood you, you misunderstood them or the are pulling your leg. I'm going with third option. Crontab is used on Linux systems to manage cron jobs which simply execute a given command at a time interval. On a Windows system it's called task scheduler. Out of the box phpBB's cron is often referred to as "fake" cron because it's not executed by crontab. Instead you have small file that will execute whatever tasks need to be done when a page is loaded. The one downside to this is you have no control when it's executed which can be an issue on a site with low traffic. You can of course use the system cron to execute it by adding it to cron jobs and changing the settings in phpBB's ACP.