How to get SAP ABAP Documentation and Examples within an SAP system?

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Execute transaction:
ABAPDOCU
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SAP ABAP Programming Essentials

To write or Edit an ABAP program/ABAP Editor/Object Navigator:
Execute transaction SE38 or SE80

To Define/Describe, etc. for Tables, Data Elements, etc./ABAP Dictionary:
Execute transaction SE11

User Interfaces creation/Screen Printer:
Execute transaction SE51

Function Modules/Function Builder:
Execute transaction SE37

How to stop individual SAP instances

It is possible to stop individual SAP instances by using commands such as:

stopsap R3 INSTANCE_NAME or stopsap J2EE INSTANCE_NAME

List owned SAP Background Jobs

Execute transaction 'SMX' to list your own background jobs with their status and other details, e.g. Start date, Duration, etc.

Quick Log off from an SAP Gui session

/nend

Execute transaction '/nend' to log-off. You will get a pop-up window saying any unsaved work will be lost. This transaction ends multiple sessions, one at a time, and gives the 'Log Off' pop-up only in the last session window.

/nex
Execute transaction '/nex' to immediately close your session.
CAUTION: Any unsaved work WILL be lost because you will not be reminded of it by any pop-up window if you use this transaction.

Various Traces

To monitor and troubleshoot, depending on the issue, execute following transactions as primary problem assessment:

ST11 - Developer Trace
ST22 - ABAP Dump Analysis
ST01 - System Trace
ST05 - Performance Trace
SM21 - System Log

Configure System Monitoring in CCMS

Use Transactions RZ20 and RZ21

External Operating System Commands

Execute Transaction SM69