Two licences
REGULAR LICENCE — use the product in ONE end product that end users are not charged for. If your users pay to access it, you need the extended licence.
EXTENDED LICENCE — use the product in ONE end product that end users MAY be charged for.
One licence, one end product. A second project needs a second licence.
What you may do
Modify the source however you like. Deploy it on a staging site and a production site for the same end product. Keep using it forever — the licence does not expire, and neither does your right to the files.
What you may not do
Redistribute, resell, sublicense or give away the source, modified or not. Use it in a product whose main value is the code itself, such as a template or theme for resale. Remove or obscure the licensing check.
Updates and support
Updates are free for the life of the licence. Support is included for the window stated on the product page and can be renewed after it.
Purchase codes
Your purchase code is proof of licence. Keep it — support requests need it, and it is how the product verifies an installation. Sharing it is sharing your licence.