Hii aspirant
Hope you are doing well amid covid-19 pandemic

Nowadays in India there are entrance exam conducted for students to get admission in best colleges in Engineering, Management, Medicine, etc
Millions of aspirants appear for these entrance exams but the seats are limited not everyone can get a seat in the top colleges so these tests are of utmost significance
So when we talk about marks it is the score which a student secures from maximum marks
Like it's a 300 marks entrance and student A scores 220 it is marks
Student B score 219  so A is 1st ranked and B is 2nd ranked similarly if X scores 150 Then he recieve a rank according to it
Percentile :-  it is a Score based on the relative performance of candidates who have appeared for thethese entrance exam. To calculate apercentilescore, the marks secured are converted into a scale ranging from 100 to 0 for each session
of examinees
It is not equivalent to percentage
Also read the following link for further reference

https://www.google.nl/amp/s/engineering.careers360.com/articles/jee-main-marks-vs-percentile/amp

Hope it helps