CentOS Modified Tutorials

When we use CentOS, find the BIOS system time is wrong, then how did this when we changed?
Methods are as follows:
[Root@Alvin ~]# hwclock-show # displays the current BIOS time
-0.826052 Sunday, June 28, 2015:12:55 28 seconds seconds
[Root@Alvin ~]# date # displays the current time
Tuesday, June 30, 2015 16:32:03 CST
[Root@Alvin ~]# hwclock-systohc # with the current BIOS time synchronization (-hctosys BIOS to sync)
[root@alvin ~]# hwclock – -show
16:33 Tuesday, June 30, 2015, 31 seconds -1.040833 seconds
[root@alvin ~]# date
Tuesday, June 30, 2015 16:33:41 CST
[root@alvin ~]#
Modify the current time is as follows:
[Root@Alvin ~]# 06/18/15 # modify the date as June 18, 2015
Thursday, June 18, 2015 00:00:00 CST
[root@alvin ~]# date
Thursday, June 18, 2015 00:00:11 CST # Note: at this time is 00:00:11
[Root@Alvin ~]# 14:20:50 # 14:20:50 time modified to
Thursday, June 18, 2015 14:20:50 CST
[root@alvin ~]#