Some of the basic questions, examples
1. Not able to set TECO to the production orders? What could be the reasons.
2. How to explode new BOM in the order?
3. Not able to Confirm the production order.
4. Not able to create BOM or routing for raw material?
Most of questions are similar to one you get in SDN forum or this forum.
Some will be custom requirements, like custom reports, enhancements, interfaces based on client requirements.
You get severity tickets in most of the cases of custom developments or standard functionality not working. Usually standard functionality not working will be rare cases, if you get it also then you can search solution for this in SAP OSS notes.
Hope this reply helps you.
Support activity means that you have maintain the system. All the activities happen smoothly without any hazzle.
Issue or ticket what user cannot do, he asks for help or support.
Types of issues -
1) How to do - like creating master data, how to do confirmation etc.
2) Rectifying the mistake - did wrong GR, how to reverse now
3) New requirements - mapping of new process
4) Enhancements and reports - as users start using the system, ask for more reports
5) Performance issue - slow running of z programs
Hope it is clear.