The features described here are designed for low vision users who can still see the screen but who find it difficult or tiring to read using their vision. VoiceOver users are recommended to avoid these features and to use VoiceOver gestures to have text spoken.
In my opinion it's worth considering using VoiceOver instead of the Apple low vision speech tools described here so long as you don't have a problem performing simple VoiceOver gestures or remembering them. It's very easy to dip in and out of VoiceOver by asking Siri to turn it on or off and then using a few simple VoiceOver gestures in conjunction with your vision to have text spoken.
If you want to try Apple's low vision speech features you'll find the settings to control them at Settings / Accessibility / Spoken Content.
There are three features offered here, speak selection, speak screen and a speech controller.
Turning on "Speak Selection" will result in the display of a speak button whenever text is selected. You may need to tap on arrows to move the displayed menu onwards to display the speak button. Use this one with caution. If you use it on text you are writing, the selected text will be deleted if you unintentionally tap the keyboard.
Here's how to select text when VoiceOver isn't turned on.
If you are typing text and want to select some of the text you have typed, double tap with one finger to select a word, triple tap with one finger to select a paragraph or tap a word and rest your finger for a while and then lift your finger. Blue blobs willappear on markers to show the beginning and end of the selection. The selection can be adjusted by dragging the blue blobs.
If you aren't entering text but reading text such as an email in your inbox you may find that only the tap and rest gesture is available.
Turning "Speak screen" on enables speaking of the screen by one of two methods. The screen can be spoken either by swiping down with two fingers from the top of the screen or by instructing Siri to "speak screen". In either case, when speech begins, a speech controller will appear on the screen. After a few seconds, it will collapse to a small button and after another short pause the button will dim so that it does not obscure content on the screen. The controller can be retrieved at any time by tapping on this button. The speech controller button can be dragged to any location on the edge of the screen and will remain in that location until you drag it again.
In the screenshot above, an email message is being spoken by "speak screen" and the speech controller is fullly visible on screen. The speech controller buttons are described from left to right. The left arrow button collapses the screen controller to a smaller button. The pointing finger button enables touch to speak mode. With this enabled, tap an area of the screen to hear it spoken or drag your finger from area to area to hear them spoken in sequence. Touch to speak mode will end when you lift your finger off the screen. The back arrow and vertical line button will move speech back a paragraph. The pause/play button will pause and resume speech. The right pointing arrow and vertical line button will move speech forward a paragraph. The 1x button can be tapped to change the speed of speech and, finally, the x button will stop speech and remove the speech controller.
This iPad screenshot shows the same email message, but the speech controller has collapsed to a dark, square button near the bottom right of the the screen. The dark button willl dim to a light grey after a second or two. Tapping it will reveal the full speech controller. The small square button may appear at a different location on your screen.
If you turn on "speech controller" the small square button to summon the speech controller will be displayed permanently on the screen. There are also two shortcuts. If you long press the speech controller button, speak screen will begin immediately. If you double tap the speech controller button, touch to speak mode will be enabled. The speech controller button can be dragged to any position on the edge of the screen.
The spoken content settings also offer a setting to change the opacity of the controller button when dimmed, a range of voices and a slider to control the rate of speech allowing you to set the speech just the way you like it.