Hello Sivyile
In XoS there are dynamic ACLs that you can execute on the cli and are usually in used until the switch is rebooted. A permanent ACL is done using a policy file. This file can be created using the CLI using the built in VI editor.
I am assuming you need the permanent version. What I would recommend is to create the file using notepad on the computer and then transferring it to the switch using FTP or the newer web management of the switch (21.x)
The best way to do this initially is to go into the concepts guide and copy the example that is in there and paste it to notepad then manipulate it.
If there is something specific you need to do with the ACL let us know and we can create it for you but need the data
Thanks
P