Amresh No worries, fetching emails is actually pretty simple. First thing you need to do is tell osTicket what mailbox it should be using. This requires the username, password and server settings and is done via Admin -> Emails -> Emails. As an example, see my setup below - the server settings are for Office 365, so you'd need to change to match your setup if you're not using this:
Probably easiest next step is to go to Admin -> Emails -> Settings and temporarily enable autocron:
This means osTicket will poll the mailbox and grab any messages from it while an agent is active. Send a couple of test messages, and they should appear as tickets after a couple of minutes (depending on the Fetch Frequency you set).
If this all works, you can then turn off autocron (leave the other two 'Enable' boxes in the screenshot checked) and set up a proper cron job on your server. This is better, as autocron only works while an agent is logged in and active. There are varying ways off doing this, but the approach I use is:
Replace www-data with the user your web server runs as. In the text editor, enter the following line then save and quit.
*/2 * * * * php /var/www/html/api/cron.php > /dev/null 2>&1
This gets your server to run the cron tasks on osTicket every 2 minutes, regardless of whether or not an agent is logged in. Of course, if your installation is not in /var/www/html/ then change the path above to match.