‘Inception’ movie walkthrough

I started watching the movie ‘Inception’ and after about 30 minutes I realized that I don’t really understand what the heck is going on.
So far this is what I got: there are layers and layers of dreams; there is a ‘thief’ stealing people’s most intimate and hidden secrets, and this thief must implant an idea into the subconscient basically. Hence the title of the movie.

I searched the net, and the best explanations regarding who’s doing what and where (dream state or reality-reality) I found to be on Screenrant.com.
Courtesy of this site, following are some guidelines that may be useful to read before starting watching the movie.

First of all, there are 5 levels of dreams:

Now the action is a little bit more clear.
Bear in mind that for Cobb (Leonardo Di Caprio) the kick is the totem. In a dream state the totem spins smoothly.

To return to reality, they need to get back layer by layer, one must stay awake in each level [Dreamer stays]. They need an “alarm” [the music] to synchronize time of the ‘kicks’.
One way to know you’re in a dream is that you couldn’t remember how you get there. When Cobb wakes up in the plane, he’s back to where he was, he’s not waking up in some unknown place with no explanation of how he got there.

When we create a dream, we fill out the scene with projections. In Cobb’s dreams, he set up projections to protect him from extractors, from other con artists like himself.
Example: Cobb and Ariadne in Ariadne’s dream. Ariadne changes the surroundings, creating paradox. Pay attention to the scene changing all the time, with stairs going nowhere, or streets folding. At some point, Cobb’s projections started to “attack” her because Cobb’s subconcious mind felt that someone is messing with his mind.