e-Devlet is awesome in this regard, I am still suprised lots of more developed countries don't have anything similar. It is like a swiss knife for healthcare, financial and legal services. The e-Devlet app is also pretty fast and the webpage does not suck.
Though I wish the signup process was simpler, because you need to go to the nearest government post office to get an account. But I guess it is like that to prevent impersonation.
It's a delightful game.
If you are self-employed, all you have to do is do the regular tax bracket income tax calculation on your net income (total income - work expenses) and add the fixed mandatory health insurance cost. It is very easy and can be done through e-Devlet or your bank's mobile app/website but many people just hire an accountant because mistakes can be costlier than the minuscule cost of hiring one. Another alternative is to get all your payments through a payment processor that handles taxes for you, which is the go-to option for side hustles.
If you are an employer, you do the same as above, but for yourself and all your employees.
For all the other extra taxes (car ownership etc.) you are notified if you owe anything and the payment is again as easy as online banking or e-Devlet. I've never heard anyone complain about the process of paying taxes. The absurd amount of taxes on the other hand...
Also, "you can sue them" in this context means "you can use e-Devlet to sue a company online, without having to leave your house". It goes straight to your local Consumer Court, who asks the company to send in their defense and then the Consumer Council gathers together to reach a verdict. This total process normally takes around 3 months and you have to do absolutely nothing once you send the official complaint online, but some companies like to delay this procedure just because they can, by sending in their defense the last day before the deadline.