Their 3 types:1)Non-Reusable,2)re-usable,3)External Action

NonRe-usable: an action that canused only in the in test in 
which it was created& used once only.

Re-usabled: An action that can called multiple time by the 
test in which it was created.
- if we need any modification we can doin the action

External : An Re-usable action that can called from the 
other test in which it was created.
- we can not do modification

In Qtp we have 3 types of actions.

1) Non-Reusable Action
2) Reusable Action 
3) External Action

Non-Reusable Action: By default each and every action in
same test non reusable action. The action is non-reusable
action we can't reuse that action script from another test.

Reusable Action: If the action is reusable action we can
reuse that action script from any test in qtp.

External Action: When we are calling reusable action from
another test it is automatically converting as external
action. if the action is external action it can't accept any
modifications.