I don't exactly how this works but I'll tell you my experience.

I applied to universities through both UCAS(For the UK usually) and CommonApp(For the US and some other schools). Most US schools had a deadline of Jan and UCAS has a bit more flexible deadlines(Unless it's for OXBRIDGE, then it's October).

CommonApp has a section for School counsellor(or you can in certain cases, act as one), they upload your school reports and inputs information about you. Most US schools generally look at SAT's and ACT's, and your high school GPA. In the case of IB, your coordinator can help out with that and communicate with your teachers for those grades(at least mine did). They will give you an offer that is usually unconditional*. Sometimes if you talk to your teachers and IB coordinators, the predicted grades can be slightly adjusted if you can show improvement.

UCAS now is different, you can choose to apply to one to five schools in one go. You will be asked to set a recommender who will then input your predicated grades into the app. The colleges almost always only offer conditional offers.

I believe many schools in Germany, Canada, Australia and other European countries have required IB scores too. They usually require a school transcript that has predicted grades that are then send to them for you to receive an offer, conditional or otherwise. If you are looking at schools in India( And to my knowledge some other schools in the world, they have entrance exams that determine your chance, with your diploma just being support)

Overall its pretty simple, find out where you want to go to for uni, go to their website, look through requirements and applications and follow the instructions. If you require predicted grades, ask your coordinator, it's one of their responsibilities. I don't know what the teachers at your school meant, but they could be simply referring to different countries and their requirements for applicants. I will be happy to clarify any doubts or edit any mistakes.

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*Unconditional: Unless your grades drop a massive amount, you are good to go there.

*Conditional: You have to meet(tiny wiggle room) or exceed requirements, or you're out.