If you want to bring your own device from the country of origin make sure that it's unlocked.
If it is - you should check which cell providers your device is compatible with.
https://willmyphonework.net/ is one of the best ways to do it before.
Once you chose an operator head to their sales point (pro tip: make sure to have 2 picture IDs with you).
Going to a central one is better - the staff in the smaller ones has less experience with newcomers.
There you can ask for a tester SIM to make sure your device is compatible.
Beware: they will try to sell you an obliging, usually 2 years, contract. This makes little sense for BYOD situation. So consider asking for a non commitment plan.