Boot Environment (BE) is a bootable instance of the image of the Oracle Solaris operating system and of any other software packages  installed in this image. Think in your particular OS, let's say Windows 7, with all your programs and updates installed on it,  creating a BE of this OS is to have all your  programs and updates saved in a partition as a file, where you can boot in case the main one in use gets corrupted for instance. However, Boot Environment belongs particularly for Solaris because it uses Z File System (ZFS).
Although your BE can be a exactly copy of your current use OS, you can also have different BEs in your system with different versions of software installed. It's good to remember that only one BE can be active at a time, like in your Windows 7, only one user can be logged in at a time.
1 - To list all the Boot Environments on the system:
reny@solaris11_2:~$ beadm list
BE                        Active Mountpoint Space   Policy Created          
--                        ------ ---------- -----   ------ -------          
sol11.1                     -             -          65.23M  static 2014-09-19 17:08 
sol11.1_bkp-1         -            -          314.09M static 2014-12-09 18:40 
sol11.1_nvidia         -            -          23.67M  static 2015-02-12 13:44 
sol11.1_nvidia-1        -           -          309.30M static 2015-02-12 13:51 
sol11.1_nvidia-2       NR        /          20.27G  static 2015-02-12 14:51 

Note: The NR means "Now & Reboot". "Now" the current BE running, "Reboot" the default BE when computer reboots. 
2 - To list all the Boot Environments on a SPARC ok prompt (OpenBoot PROM/OBP) you should use:
ok boot -L
3 - To boot into a BE from the ok prompt (OpenBoot PROM/OBP) on a SPARC:
ok boot -Z rpoll/ROOT/solaris-03312015
4 - To create a Boot Environment (a copy) of your current one. Note: You have to be in the BE that you want to copy to run this command!
reny@solaris11_2:~$ beadm create solaris_backup
5 - To clone a specific Boot Environment, meaning the one you are not running:
reny@solaris11_2:~$ beadm <name of a specific BE> -e <a name for the clone>
reny@solaris11_2:~$ beadm sol11.1_nvidia -e mysol_clone
Note: When Creating/Cloning, a BE name cannot be a boot environment name that is already being used, use your imagination :) If it's just backups you could use the date for example (solaris_31032015).
6 - To activate a different Boot Environment as default. Depending on your settings you may need to be root to run this:

root@solaris11_2:~# beadm activate sol11.1_nvidia-1
root@solaris11_2:~# beadm list
BE                                  Active Mountpoint Space   Policy Created          
--                        ------ ---------- -----   ------ -------          
sol11.1                                 -          -          65.23M  static 2014-09-19 17:08 
sol11.1_bkp-1                      -          -          314.09M static 2014-12-09 18:40 
sol11.1_nvidia                      -          -          23.67M  static 2015-02-12 13:44 
sol11.1_nvidia-1                  R         -          12.20G  static 2015-02-12 13:51 
sol11.1_nvidia-2                  N         /          8.42G   static 2015-02-12 14:51 
sol11.1_nvidia-2-backup-1  -          -          246.0K  static 2015-02-25 13:26 

Note: Pay attention that now the BE "sol11.1_nvidia-1" receives the "R", meaning next time computer reboots that will be the  default BE to boot.
7 - To destroy a Boot Environment to create more space on your system. Note: You cannot destroy the BE that is currently booted:
reny@solaris11_2:~$ beadm destroy sol11.1_nvidia-1
8 - Changing the name of a Boot Environment. Here I'll change the name of the third BE "sol11.1_nvidia":
root@solaris11_2:~# beadm list
BE                                   Active Mountpoint Space   Policy Created          
--                        ------ ---------- -----   ------ -------          
sol11.1                                 -        -          65.23M  static 2014-09-19 17:08 
sol11.1_bkp-1                      -       -          314.09M static 2014-12-09 18:40 
sol11.1_nvidia                      -        -          23.67M  static 2015-02-12 13:44 
sol11.1_nvidia-1                   -        -          309.30M static 2015-02-12 13:51 
sol11.1_nvidia-2                   NR     /          20.27G  static 2015-02-12 14:51 
sol11.1_nvidia-2-backup-1   -        -          246.0K  static 2015-02-25 13:26
Changing to "be_nvidia"
beadm rename sol11.1_nvidia be_nvidia

root@solaris11_2:~# beadm list
BE                                Active Mountpoint Space   Policy Created          
--                        ------ ---------- -----   ------ -------          
be_nvidia                              -      -          23.66M  static 2015-02-12 13:44 
sol11.1                                   -      -          65.23M  static 2014-09-19 17:08 
sol11.1_bkp-1                       -      -          314.09M static 2014-12-09 18:40 
sol11.1_nvidia-1                    -      -          309.30M static 2015-02-12 13:51 
sol11.1_nvidia-2                   NR     /          20.27G  static 2015-02-12 14:51 
sol11.1_nvidia-2-backup-1   -        -          246.0K  static 2015-02-25 13:26 

Whenever and whatever you do regarding the Boot Environment using the beadm command, it automatically manages and updates the GRUB  for x86 systems or the boot menu for SPARC systems. Click here for more information in Boot Environment.