Buying bicycle : What is the Difference between cheap bikes and expensive bikes ?

Two days ago I went to Carrefour looking for a bicycle. However, I am confused there are so many types of them. So, I decided not to buy at that time. Instead, I went to look for some general information regarding the bike. As usual I googled and found a lot of info but I got one which is useful.

Here is the website link http://handsonbike.blogspot.com/p/cheap-vs-premium-bikes.html 

The writer seems to have a good knowledge of bicycle things. His explanation is very comprehensive. It is worth reading if you want to know about the differences between cheap bicycle and premium one. Just go to that website link above.

However, I have not decided which bike I would buy. I think I will explore other bike stores because what are offered in CF is not many......I might should contact the guy from whom some people in office bought bicycles  last month.