[otrs] What are SLA and Services?

I have been looking for an explanation to what the SLA and Service options do. I haven't been successful in finding anything in the manual or on this list. I would like to be able to understand the full functionality of OTRS and these options have been alluding me. Could anybody point me in the direction of an example of what these are used for and how to go about using them? I have been successful in how to enable them using sysconfig and found them in the admin module. I appreciate your help. TIA

~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~>~> Craig Meirick, Help Desk/PC Support Northeast Iowa Community College -- http://www.nicc.edu <~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<~<