The first thick one might be a level that comes from some other action, but just based on this chart, it is a level that price couldn't cross.
Each successive line shows first a level where enough buyers first stepped in to drive price up, and then a level at which buyers were unwilling to buy and sellers were able to overwhelm them. (dare I say first the lines act as support and then as resistance!)
The lines also divide the areas of consolidation so to speak, areas where not many trades happened as price moved between different levels of consolidation.
I would perhaps state the above with different words, meaning mostly the same thing as stated above. Each value area or where price was supported by buyers coming in is successively lower than the previous one, showing a down trend in price.
This continues until the last horizontal line. It's here that the buyers chase price back up into the previous value area and sellers keep raising their offer price. The first time this previous value area is 'revisited' might be an occasion to perhaps anticipate a shift in the demand and supply dynamic. Maybe, just maybe the buyers are more eager to pay the prices offered by sellers, and sellers sensing this are raising them. Could this continue? Meaning would buyers chase price higher to another value area above the current one?