iOS icons

So I am just starting to build my website with Highend. I don’t know what most of all these settings are. Don’t you have a dictionary/resource to explain the 100s of settings? How are we supposed to know what all of these settings mean?

For example, I am on the Dashboard –> Appearance –> General Settings. It has me upload all these icons in particular pixel sizes as a png or gif. First of all, what is a bookmark? Is it the tiny icon next to the tab with the name of the website? For example, HB Themes’ icon is a box grid?

Secondly, why are there two pixel sizes for non-retina iOS devices and two pixel sizes for retina iOS devices? Are we just to choose one size?

Thirdly, my icon will be as a jpeg. Is it easy/possible to convert to png and how do we make it that exact size?

Fourthly, what is site preloader?

What are breadcrumbs? What are the two pagination styles? What is tracking code? Custom script?

Thanks.