Here is quick step to upgrade Oracle Applications from version 12.0.0 (Base Release) to 12.0.2 (Release 12 Roll-up 2)
Things to Note for 12.0.2 upgrade
1. Oracle Applications 12.0.2 can only be upgraded from base release 12.0.0 or 12.0.1 , If you are on previous version of Oracle Applications (10.7, 11.0.3 or 11i) first upgrade it to R12 base release (12.0.0)
2. If you have not already applied minipack AD.A.2, first apply R12.AD.A.2 (6014659)
Before Oracle Applications R 12.0.2 Upgrade
1. Download Patch 12.0.2 from metalink (5484000)
2. Download AD Patch R12.AD.A.2 (6014659)
Upgrade Steps
1. Shutdown R12 Application Tier using script adstpall.sh under $ADMIN_SCRIPTS_HOME ($install_base/inst/apps/$SID_$HOSTNAME/ admin/ scripts)
2. Enable maintenance mode using adadmin (similar to 11i process)
3. Apply patch 6014659to upgrade your AD minipack to AD.A.2
4. Apply 12.0.2 patch 5484000 using adadmin
5. Disable maintenance mode using adadmin
6. Compile invalid objects if any in database using utlrp.sql or adadmin
7. Start Application Tier of R12 using script adstrtal.sh at $ADMIN_SCRIPTS_HOME
8. Test Application
If you missed my previous Oracle Apps R12 posts here are few links
Technical Difference between Oracle Apps 11i & R12
File System Changes in Oracle Applications R12
Install Oracle Apps R12 on VMWare linux
Start-Up/Shutdown Scripts in Oracle Applications R12
Unified APPL_TOP in Oracle R12 : New Feature
Prepare Database Uprade for 11i to R12