Account admins can masquerade as (become) any user in their account, which is essentially logging in as the user without a password. You will be able to take any action as if you were the user. However, the actions you perform on behalf of the user are catalogued.
Account admins can masquerade as a user from the Users page.
Note: Some features may be restricted based on permissions for your user role.
Open Admin Menu
In the Global Navigation menu, click the Admin icon. Then, click the Users & Permissions menu option.
In the Users & Permissions menu, select Masquerade.
Note: The Global Navigation menu may differ depending on what is enabled for your account.

Become User
Type the name of the user and click the Become button.

The bar at the bottom of your browser window indicates you have become the user.
Stop Masquerading

To stop masquerading as the user, click the Stop button.