The app is called Friends Aloud. There's a free version and a paid version that allows you to post on Facebook with your voice. I suggest you try the free version first to get a taste of it.

Once you've signed into your Facebook account in the app. Tap the "Read Aloud Now" button.

The app will start to read the posts on your Facebook feed to you in a pretty plesent voice which is one of the reasons I like this app so much. It doesn't sound like a robot voice reading to you.

In the settings you can adjust how many comments in a post you'd want to have read out loud.

Below you'll see the controls. You can pause, jump to next post or go back to the previous post. Another cool feature is the button at the top right corner. Tap this and it'll only read new posts.

Go into the "Mute Friends" section and you can mute the people you don't want to listen to out loud. I like this because there are some in my friends that I really don't know well.

While you're listening and hear something you want to comment on. Tap the keyboard icon on the bottom left of the feed page and you'll be able to type your comment.

Or if you've purchased the paid version you can tap the microphone icon on the bottom right and just speak what you want to post. It'll be converted into text for you.

The app can also work in the background. While its reading your feed aloud you can close the app, browse around your iPhone and still continue to listen to your Facebook feed.

A little tip while it's playing in the background. If you double push your home button to open the background apps and swipe to the right. You can control (pause, forward, previous) the friends aloud.