An Injective Wallet is the wallet you will need to interact with any application built on Injective, including Helix. It is the more broad wallet that is needed in order to interact with the Injective ecosystem.
A Trading Account is the account that is needed to make transactions on Helix. You will need to transfer funds from an Injective Wallet into your Helix Trading Account in order to place orders on any Helix market listing.