Activating Changelists 
The changelist that you want to activate must contain change versions and have the status Open.
Call the Change Organizer.
Mark the changelist that you want to activate.
Note
You can select multiple changelists to activate them at the same time.
Select Activate.
If the changelist has a generically-produced name, change it to a more meaningful name in the Activate Changelist dialog box. Otherwise you cannot activate the changelist.
Note
Using system settings in SAP NetWeaver Administrator, you can control if the entry of a new name for a changelist is enforced or not. This is set up by default and is recommended to keep the names of changelists meaningful.
For more information: Configuring the Change Organizer
You have the following options when activating a changelist:
Activate
If you activate the changelist but do not want to attach it to a transport request, choose Activate. The changelist gets the status Activated and can be attached to a transport request at a later time.
Activate and Attach to Transport Request
If you want to activate the changelist and immediately attach it to a transport request, choose Activate and Attach. The dialog box Attach Changelist for Transport opens where you can attach the changelist to a transport request.
For more information: Attaching Changelists to Transport Requests