In QTP, default mode is per-action. We have a multiple
actions  within the same script, each and every action
contains separate object repository. In per-action both
script and object repository both are tied with each other.

     If you choose as shared object repository, all actions
contains only one object repository. We can use this object
repository to any actions, and memory is also save. Here
script and object repository both are independent with each
other.

     Go to test menu --> click resources tab --> you can
view shared or per-action object repository.(In QTP 8.2 version)

Navigation: 
   test--> settings-->resources tab-->in that we will have 
per action,shared.

PER ACTION:
  .when we r working with single action tests
  .we except tht the obj will not modified continusely
  .if we r new to quick test and performing simple 
recording and play back then select per action type

SHARED:
   .if we r working with multiple tests
   .we except tht the obj  r modified continusely
   .if we have less number of obj and more test scripts
   .if we r expatised in quick test then select shared type

tools >options