Practice them until you master them. Observe only the initial sound, it is the only combination that is presented for /ɕ/ and /ʂ/. Both are fricative, but the /ʂ/ is retroflex, it is the same point of articulation but this is produced by curving the tip of the tongue towards the throat. Press the button for the pronunciation you hear. The button to identify what you hear has the IPA characters, and the label below it the corresponding Pinyin in red. In the image you can see the difference, and the blue line shows you the frequency variation for the tone.