To Install the App you will need an iPhone or iPad device - or MacOS device. You will need to install it by visiting the App Store.
Go to settings. Go to Language and Voices. Choose an offline or online voice. You can hear a preview of the voice by tapping on the play symbol next to each voice - and you select them by tapping on them. Once done, slide the menu down. To remove a voice make sure it is not the active voice (with a tick) and then swipe right to remove it.
You can either tap on "Edit" and then write some text - or press the + button in the upper right to add a text file you can find on your browse.
Tap on a word in your text block, and it will play the Word/Sentence/Paragraph/All of the text - depending on what is selected in the bottom left menu. Change that option, then tap again to see it speak that text again.
Press the play button - and it will then read the next element (word/sentence/paragraph) until the whole text is finished.