diversity - variety

What is the difference between "diversity" and "variety"? And also "selection"?

There is only a slight difference between 'variety' and 'diversity' but I'll try to explain anyway.
'Diversity' is usually used when speaking about people or a species (of plant or animal). For example: There is a lot of diversity at this university. Meaning that many cultures/races/ethnic groups are represented by the population. Or: There is a large diversity of plant and animal life here.
'Variety' is used when speaking about a choice (from which you can make a 'selection'). For example: There is a large variety of fruit here. Meaning, there are many types of fruit to choose from.
'Selection' means a collection of things that have been chosen. 'A selection of fruit' means that you have taken some fruit out of the 'variety' of fruit that you had to choose from.
That's really a lot to take in for a non-native English-speaker so I'm sorry if that didn't help!

Diverse is a synonym of various, both being the root words of diversity and variety. You can use both interchangeably.
(synonym meaning they mean pretty much the same thing)

It's not uncommong to hear Diversity in more of a multi-cultural context, although you can use it in the same places as variety.

A section is a chosen set much like Nick(russian keyboard switch no want to work) said.

Within a diversity(variety) of items you pick(choose) your selection.