A package is an amount of traffic, in GB, that you buy up front. It runs for 31 days from the purchase. Traffic that passes through your proxies counts against it.
Open Proxies › Residential and press Manage on a package to see what is left, when it ends, and the login for it. Each package has its own username and password; the host and port are the same for every package. Buying another package does not touch the ones you have.
A package is not renewed and cannot be topped up: when it ends or runs out, buy a new one. Traffic left at the end does not carry over.