Read aloud gives you a short text, about forty seconds to prepare, and then records you reading it. It contributes to both your reading and your speaking scores, which makes it the single best use of practice time in the exam.
The algorithm is listening for three things, and they are worth different amounts.
Oral fluency. Continuous speech at an even pace, without restarts. This is where most marks are lost. A student who mispronounces a word and carries on scores better than one who says it correctly the second time after stopping. Never go back. If you stumble, keep moving.
Pronunciation. Individual sounds, judged against how the software models English. You do not need a British or American accent — Indian English is fine and is scored fine — but word stress matters, and so do the endings Indian speakers commonly clip: the -ed and -s at the end of words. "Developed countries" has two endings in it and both carry marks.
Content. Every word you read that is on the screen counts. Skipping a word, adding one, or substituting one loses content marks even if the sentence still makes sense.
How to use the preparation time. Do not just read the text silently. Find the punctuation and plan your pauses, spot the two or three words you are least sure of and decide how you will say them, and notice any long noun phrase you might trip over. Then read it once in your head at speaking pace, so the first time you say it aloud is not the first time you have processed it.
When the microphone opens, start within a second. PTE stops recording after about three seconds of silence, and a slow start can end your answer before it begins. This catches a surprising number of candidates who are still composing themselves.