Explorations sort of makes it sound like what went on during the early-modern and modern European age of colonization. But Greek colonization was pretty different. And really colonization is a bad word to use because of the later implications.

They essentially set up new city-states in new areas. They city-states might have a cultural connection with their mother city (metropolis) but they weren't directly ruled by them or share any governing. Colonies were often given some partial treatment in diplomacy by a metropolis but even then not always. In fact citizens of a new city-state couldn't even attain citizenship in the metropolis. Some of the new colonies grew to be large and hugely influential city-states in their own right. They weren't just some backwater (not to imply that colonies in the modern age of colonization were backwaters).

The Greeks also didn't usually take over the surrounding area of where they settled. They usually set-up a city and had some area surrounding it to help support it, which was more or less the model at home. I can think of some exceptions more in the post-Alexander world. But that was generally the rule.

Their motivations were varied. Greek city-states could have a lot of political unrest and some of the people in new colonies were people being ostracized from the metropolis. Greece is also an area with limited arable land so as populations grew they had to find new outlets. But, really, the biggest motivator for colonization was facilitating trade. Creating a loosely aligned, independently governed network of city-states on valuable trade routes was already a Phoenician model.

They did get around. There were Greek colonies as far west as the Iberian peninsula and as far East as the Baltic Sea region of Turkey. They even got into Russia. I don't know much about their reactions to places. The thing is while they did go relatively far for the time they probably wouldn't have encountered too much that was unknown to them. Most of the areas were likely places they had contact with because they were on trade networks, in fact that would have been a likely reason to settle there in the first place. As an example, Tanais was a Greek-city state in what is now Russia (sort of, let's not worry about that). It was pretty far up on the Baltic sea. And life there was probably pretty different from mainland Greece. However, the Greeks likely had some contact with nomadic traders in that region for a very long time. They had likely been traveling there to meet with those traders (likely to get furs and other items) for a very long time. So, there wasn't much to shock or surprise them about conditions.

I really dislike this map because it makes it look like the Greeks or Phoenicians controlled all of the area that's highlighted. Which is not correct. They had city-states in those areas. However, it does give you an idea of how far they traveled.

https://mapcollection.files.wordpress.com/2012/06/greek-phoenician-colonies.jpg