The word "vary" is used when there are differences among things or people. When they have different qualities and features, they vary.
simple
past
past participle
vary
varied
varied
The climate in California varies. It depends on where you are in the state.
Results from our experiments varied. (We got several different results.)
Opinions on the topic of gun control vary.
There are varied opinions on this topic. (The word "varied" in this sentence is an adjective.)
His account of what happened last night varies from her version of events.
The personalities of the children in that family vary.
Related to the word "vary" are a few other words. The first one is "variety." The word "variety" is a noun. Use it when talking about many different things:
There’s a variety of fruit and vegetables at our local grocery store.
There isn’t much variety on this radio station. All the music sounds the same.
There are several different varieties of paint to choose from at the hardware store.
The word "various" is an adjective. This is a popular word to use when describing differences:
Picasso mastered various styles in creating his artwork.
Mary gave various reasons for why she was late, so no one believed her.
In our backyard we have various trees and plants.
The artwork at this gallery varies.
There’s a variety of artwork at this gallery.
(Note: The word "very" is an adverb. This is a completely different word.)