My pronunciation of putonhua isn't perfect but I'll give it a try.
'j' is pronounced ch as in cheek. E.g. zai jian: goodbye (pronounced dza'i chi'eN)
'zh' and 'ch' sound like ch too, only sharper.
'X' is the german 'ss' which is written like the beta symbol. Non-natives usually pronounce x like sh but a chinese vlogger insisted there was a difference.