Trading account is optional.
If you want to use only social features to connect with your friends you can remain with a social account. The social option is also good if you’re not yet sure whether you want to start investing your money. In such a situation a social account is a perfect choice as it will allow you to track others' activities, discuss market opportunities, create your own chats or join the existing ones.
However, to invest your money in various assets that are available at Shares, you will need to create a trading account and verify your identity, as it’s not possible to trade using a social account.