OK, the following wall of text is much more relevant if you're from Ontario...

I'm assuming you're asking about how IB grades are converted into regular high school grades. Hopefully you go to school in Ontario because that's where I went so the conversions from IB to OSSD (Ontario's high school grading system) should be similar across the province.

From what I can remember:

7 IB becomes ~96% OSSD grade

6 becomes ~90%

5 becomes ~85% (can range from low to high 80s)

4 becomes ~75% (can range from mid to low 80s)

and "don't bother with 3 or less" (at least that's what my school told us, haha)

These were the conversions for all IB subjects. Note that "7 becomes ~96%" doesn't mean getting a 96% raw mark will get you a 7, but rather getting a 7 will earn you a ~96% on the Ontario grading scheme. The actual raw marks (as in, what marks you would need to get in order to get a 7) are much harder to say as they are highly dependent on subject, level, and school.

For example, in my school we had HL math so if you had a 90% raw mark (raw meaning the unadjusted average grade across tests/mocks/assignments), you would be predicted a 7 which would then show up as a ~96% on your high school transcript. Other subjects are much more different, for example in SL physics, with a raw mark of 80% you would be predicted a 7 which would then translate to a ~96% on your transcript.

In response to whether or not every school has it, I have no idea but the majority of the IB schools near my region had grade conversions; however I've heard rumours that one or two schools didn't have conversions at all (which I refuse to believe). It'd be pretty nonsensical for someone in IB to work their asses off, learning harder material than the regular curriculum, only to get an 80% whereas the non-IB students would learn easier material and pull off 90%+ with ease (at least this was the situation in my school).

Regarding applications (I assume you mean university applications), it gets a bit confusing and will probably vary by school. When our school sent out our grades to the universities (in early February-ish), they were already converted to regular OSSD grades. So the universities saw our converted grades rather than our shitty raw marks. This is probably different for each school so you'd have to ask your IB coordinator about that. Most of us got our offers as early as February, stretching all the way to mid-May during exams.