IOI is an International Olympiad Competition in Informatics (Computer Science). Each country sends 4 participants to this international competition with 1 or 2 participants as reserves. Each country has their own process on how they select these top 4 participants that represent the respective country at the IOI.
Each country has a series of qualifying competitions, exams and training camps that will enable them to select the final four participants. So, not only is the IOI the ultimate prestigious competition, but even the selection exams towards the IOI are also prestigious national level competitions. These are definitely difficult exams primarily concentrated around computer mathematics, number theory, graph theory, algorithms, and competitive programming. So, students will have to warm themselves to the standard by giving the initial exams first and preparing for each for the selection exams in their respective country.
Coding Olympiad Process for India:
The Zonal Informatics Olympiad, 2023 (ZIO-2023) will be held on Sunday, 4 December, 2022. Registration will open around 1 October, 2022. Students can apply for the ZIO exam 2023 in online mode on www.iarcs.org.in. Students can appear for ZIO 2023 exam at their allotted exam center. They can check admit card to know address of the exam center.
For example, Zonal Informatics Olympiad was held at 35 cities across India on Sunday, 5 December, 2021. 552 students registered for ZIO-2022, of whom 402 wrote the exam. 124 students have qualified through ZIO-2022 for INOI-2022.. ZIO-2022 was conducted in cooperation with TCS iON, a division of Tata Consultancy Services.
After the ZIO 2022 exam, selected students will appear for Indian National Olympiad in Informatics (INOI 2023), which is the second round of selection, in which students have to practically program in C++. So, from the 100 plus students selected for INOI, approximately 30 students will be selected for the IOI Training Camp (IOITC). A series of training and selection exams will be conducted at that IOITC to select the top 4 to represent India at IOI. Most of the other countries have a very similar selection critieria with a series of exams and then followed by a camp to train and select the top 4 to represent at IOI.
International Olympiad in Informatics (IOI) is going to be held in Hungary in 2023. More than 80 countries participate in IOI and send their top students every year to this competition. Each of the 80 plus participating countries will host the IOI for a particular year.
UnicMinds provides the Foundation in Computer Mathematics & Algorithms (FICA) course which serves as a strong foundation to prepare for these competitions and other similar competitions. You can find the detailed syllabus for IOI here.
You can also find country-wise IOI details in this Quora thread here.
Hope this is useful, thank you.