You can use the command date to check and set the date and time on your server. Type man date to get an explanation on how to use this command.
To keep your server date and time up-to-date permanently you can create a cron job which executes the commands rdate and hwclock at regular intervals.
More info here
You will need shell access to use these commands. If you don't have sufficient rights on your server to execute these commands you'll have to contact your server administrator.