The normal line has four parts: ip, port, username and password. Any program with a proxy field uses that line directly.
Some programs have no username and password field. For those, authorize your connection's IP. From then on the address answers to that IP without asking for a password.
An account accepts up to twenty authorized IPs. You can type one in the panel or use the button on the My IP page, which authorizes the address you are visiting from.
When you change connection, the IP changes and the old authorization stops working. Authorize the new one and, if you want, remove the old one so it does not take one of the twenty slots.