To use the app on your tablet, you should first create a Pulse SMS+ account by downloading the app on your phone, then going through the signup instructions.
Once you have signed up for a Pulse SMS+ account, you can log in to that account on the tablet. Your tablet will receive any messages that are received on the phone app. You can send new messages, reply to conversations, and do any tasks that you would have done on the phone, on the tablet.
If your tablet has its own phone number, there is an article discussing how Pulse SMS works with two devices, each with its own phone number.