I know they landed at southern Italy, and it was successful but it was a hard fought campaign, i heard mostly from the terrain, why didin't they choose another spot, like in Dalmatia or Genoa areas?
This is only part of the answer, but here goes:
Landing areas were choosen in part because they could be covered by land based aircraft. Thus beaches in southern Italy were chosen, because they could be covered from bases in North Africa, Malta and later Sicily. By the time the allies had moved far enough up the Italian peninsula to contemplate a landing further north all available resources were concentrated for landings in southern and western France.