Microsoft MVP Tom Arbuthnot talks about the control of the Administrive side in his blog here, in this post i'll show you how the user experience looks for a user that has the feature enabled within their Teams client.
Your Teams client should inform you the feature is now available to you. It will be turned on by default so you will immediately benefit from the feature.
If you want to disable it, simply go to 'Settings' | 'Privacy' and you can disable it if you so wish.
If a user you are chatting with hasn't got the feature, even if they see your message your icon will only ever show as 'Sent'. Which is a little dissapointing. You can see in this shot the user has responsed and obviously seen my message but if they hadn't of responded I would have been none the wiser.
However a user that has been enabled for the service will have read receipts working in your favour. You can see from the below screen shots that the message goes from 'Sent', to the eye emoticon that designates 'Seen'.
The feature works well, although I expected it to work and provide receipt clarity on users that aren't using the feature, however I expect it will update and improve over time.