There is no difference between ш and шь. Phonetically, ш is always hard. The choice between ш and шь in writing is determined by tradition. Other consonants that are always hard are ж, ц. Some consonants are always soft: ч, щ.
The distinction т/ть, on the other hard, is a real thing. But I don't have much advice, unfortunately. I'd suggest you just kept listening more.