faced was to simplify and present the words to children and help them grasp things easily
What they asked you to do, was to Tell them more about one of the activities you listed above, explaining what your goals were, what you did to pursue them, the results achieved, and what you learned in the process. i think it will be better if we break it down.
Tell us more about one of the activities you listed above: i assume you listed volunteering.
explaining what your goals were: what i got from the text was that your goal as a tutor volunteer is to share and spread knowledge among students as much as you can.
what you did to pursue them: by simplifying and presenting the words to children and help them grasp things easily.
the results achieved: that's the thing i didn't really saw very clear on this text, did you achieved your goals as a volunteer tutor? were you able to simplify and present the words to children in order to help them grasp things easily? universities want to see that you achieve the goals you put for yourself.
And what you learned in the process: i know is there, but is not as clear as it should be. i'm my humble opinion.
Another observation:Because of the "and and" presented in this sentence: One of the major challenges I faced was to simplify
and present the words to children
and help them grasp things easily. i would rewrite it like: One of the major challenges I faced was to simplify and present the words to children in order to help them grasp things easily.