It doesnt seem that long ago all SAP notes needed implementing manually including any code changes, table/fields creations etc.
The Note itself was pretty much the same as it is now, especially when viewed as a SAPScipt document. The note would still describe the symptoms, any pre-requisites; list all objects affected and describe the changes required but instead of being able to click the process button to implement the note (in most cases) you would have to go through every change to each object and add the code manually by modifying the SAP standard code yourself.
But now the majority of notes can be implemented via transaction SNOTE with the click of a few buttons. All the ABAP code instructions are then implemented into your SAP system. Some things still need to be created manually but this list is reducing all the time and SAP can create most things for you now.
You may still have problems if you have made any modifications to SAP standard code but SNOTE offers you the split screen editor in these circumstances to help you apply the note correctly around your modifications.
SNOTE (SAP Note Assistant)
If you want to implement an OSS note into your SAP system you do it via the SAP Note Assistant
Download SAP OSS Note
Download OSS note to your SAP system
Check OSS Note valid for your system
Check implementation Status to see if note is valid for current system and suport level
SAP Note Implementation status details
Implementation Status also see Processing Status
Implement SAP OSS Note
Implement note correction to your SAP system
View and Search all SAP notes
Find information for every availabel SAP OSS note
Example processing of Note 379269
Check if already downloaded and what it's process and implementation status is
Search for information on any SAP Note