Once you have registered you will be asked to complete the short survey and select preferable plan, after that your trial period starts.
Now follow the next steps to set up your Seller Assistant's account:
Connect your Amazon Account
Connect Google Sheets
Start researching products with Seller Assistant.
You will be able to use the extension without any restrictions if you complete all registration steps.
Note that Seller Assistant will work even if you don't connect Google sheets and Amazon account but be aware that some functions of the extension will be limited.