You can reach the Server Processes window via the Enterprise Manager and the Activity node. Double clicking the Processes node will open a window similar to the one below.
The Oracle Server Processes window, processes grouped per workstation
From this window, you can view active sessions on your Oracle server and kill the sessions if you have the privileges to do so.
As you can see in the above screenshot, there are 4 different views on all processes. Three of the tabs offer grouped lists of sessions, making it easier to see what's going on.
You can kill a process by using the Kill Process button or right click a session and select Kill Process from the popup menu.
The window will automatically refresh itself each number of seconds as is shown in the spin-edit, unless the Paused check box is checked.
You can sort the sessions by clicking on the header bar columns.
Note:
The user you used to register the server needs to have access to views V$SESSION and V$PROCESS for this feature to work.