The transportation system in Czechia is one of the best in Europe. It is clean, perfectly on time and affordable (especially for students!). It is really easy to use, but since it might differ from what you're used to, I will guide you through it. As an example, I took my expected with Prague transport. There may be some distinctions with other Czech cities, but the system's core is definitely the same.
Let's get to it!
First of all, nobody checks your ticket when you are going into the transport, and there are no turnstiles on the metro either. But it doesn't mean you don't need a ticket. Inspectors may check you, and the absence of a ticket will cost you 1525Kč (~60€). For comparison, the 1-year pass with a student discount is 1280 Kč (~50€). So, as you see, obeying Czech laws is much more advantageous for your wallet. You never know where inspectors will check you. You can meet them 3 times in one day and then don't see one for a few months.
Unlike in most cities, you don't have to worry about buying multiple tickets and paying more when transferring between metro, trams and busses. You only need to calculate the time required to get to your destination. It is simple with the IDOS app, available in Czech and English. You have to select the station you are going from and the station you are going to. If you don't know the names, you can use Google Maps, but I would still recommend getting used to IDOS. The information there is much more accurate.
There are 30/90 min and 24/72 h tickets. But if you plan to stay in Prague long, I recommend the passes I mentioned earlier. You can buy a pass for 1 month, 3 months, 10 months and 1 year. Since I study in Prague, I would prefer to buy a year pass. Even if you don't use public transport daily, you don't lose money, with a pass one day of usage costing about 5Kč (0.20€).
Another aspect you need to pay attention to is zones. The city is a P zone, nothing complicated, but if you live in smaller towns nearby, you should check which zone this city is located in.
How to buy a ticket.
A paper ticket can be bought through a ticket machine that is located in front of metro entrances and inside busses/trams, ticket windows or tobacco shops. If you can't speak Czech, I would recommend using the machine since they have more language options. You ca
n pay by cash or card everywhere except when buying a ticket inside the transport (e.g., bus driver). There is also an app that allows you to skip the line and buy a ticket online. It is called "pid lítačka" and is available in Czech, English and Ukrainian languages. It's pretty easy to navigate.
You are expected to have a valid ticket when you step inside the transport. A paper ticket is valid from when you compost it (or buy it inside the vehicle). The online ticket is activated in the app manually and takes 2 minutes to become valid. Please keep that in mind. You'll still get a fine if checked before activation is finished. I got my first and only one when I had 30 seconds until activation, so be careful. Don't be afraid if you have a valid ticket but do not have it with you for some reason. You will get a fine, but it can be reduced to only 50 Kč (~2€). The condition is to prove that you had a ticket when the inspector checked you. Fines can be paid at the spot or later online/in the ticket office.
I hope this guide was helpful. Enjoy your time in Czechia, and don't dodge the fare!
If you still need more information about travelling in Prague, read Dana's blog article.