Overview of Proxies
Assume you're on vacation or busy with work, but you want to take care of some tasks. You can designate a proxy so that someone else can sign in and do the tasks on your behalf in an impersonation session.
How Impersonation Works
Your proxies can sign in using their own passwords, and start an impersonation session. They have unrestricted access to your account, except that they can't change your preferences. By default, everything your proxy does is audited. If a business object isn't set up for audit, your proxy can't work on the business object. So you can ask your administrator to disable auditing using the Audit Impersonation Transaction Enabled (FND_AUDIT_IMPERSONATION_TRANSACTIONS) profile option.
When you sign in, you can see all the work your proxy did for you. Also, you and your proxy can sign in and work at the same time.