Travelling on the trams and buses without a validated ticket is a crime, You will be treated as a criminal of you fail to comply - everyone gets the same treatment ... you;re not being "picked on" or "singled out" because you're a visitor, nor should you expect to be let off because you're a visitor ... ignorance of gthe rules is no excuse.
Because so many people seem to be incapable of doing the sensible thing and checking the rules before they come here, I'm making this post - I hope someone will help me get it pinned. It's general information, but the principles hold good in most Polish cities, so ...
Most tickets are sold in shops and kiosks as well as at ticket machines and occasionally on board. Use the shops and kiosks to buy yours, adn machines may be broken and that will NOT be acceted as an excuse..
Tickets are more often than not for a duration - ie you buy a ticket which is valid for 20 mins, 30 mins, 45 mins, etc, depending on how long your journey will take. The clo0ck starts running when you validate the ticket - you have x minutes to complete your journey. If your time runs out you need to validate another ticket or get off.
You need to validate the ticket as soon as you board the bus or tram. Do not dither - have your ticket ready and spot the machine when you board. Inspectors are watching, and they're paid to catch you, not explain or give you a second chance.
You can avoid most of this by buying a ticket valid for 24, 48 or more hours from validation. You then only validate the first time you use the ticket and then just keep it handy for when the Inspectors ask to see it.
Some cities have two or more fare zones - typically, zones 1 and 2 are equivalent to inner and outer city. In Krakow, for example, all the tram lines are within zone 1, but you need an agglomeration ticket (two-zone) if you go further out.
So - buy ticket - board bus or tram - validate. 3 steps, simple.