[otrs] Service items is not shown in ticket form

Dear all I'm really new in OTRS. I like this application since it helps to manage the IT problems in my company. Now I just installed the ITSM modules. I saw new fields are added in the ticket form, e.g. Service and SLA. I added Services and SLAs, but when I create a ticket, I don't see the Service and SLA list of values in the combo box. I really appreciate anybody who can give the solution of this problem. Regards Rudi