After purchasing, you'll have to point your domain to the nameservers associated with this hosting. You'll be provided with nameservers addresses in your welcome email, containing also your access details.
You can still take advantage of the discount code inside the original post. That is meant for users coming from the board to purchase this service with a little saving.
All payments are subject to manual review and approval before leading to generate your hosting account and sending out your login information. This usually takes no more than 24h by the time of your payment.
Currently, the two plans offered for SharedServers accounts will provide you with the same features, with the only exception of disk space. If you need more than 5 GB provided with VALUE plan, then the EXTENDED plan is recommended.