Hello,
take it easy as that altimeter set (29.92 as standard value) is typical US system and HPa is rest of world where US system isn’t typical for use. Just one point, there is transition gap between transition altitude and transition level that do right things between going down through TL (reporting altitude on standard press QNH 1013 HPa) to altitude reporting on local airport QNH (down to approach airport) because logically local QNH can be higher than standard in some cases. You need to know airport QNH at t/o and app of airport to have all same altitude with other traffic +/- during procedure. Over specific altitude you set your altimeter gauge press to standard press (29.92 or 1013) and report FL no altitude. Sometimes is very important to hear ATC or traffic to understand because some aircraft can report f.ex. N67565 inbound LNZ 10000ft QNH1013 what points to standard press but no TL report so this aircraft is on QNH 1013 still at altitude reported and no on TL, it can point f.ex. to TMA transition with departure or arrival procedure. That TL is defined specifically from Country to Country but is logical that neighbored Countries have own specific DEP/ARR procedures of press set due maybe different requirements/rules about TL definition when aircraft comming/leaving it’s areas.