After a painful night, I finally succeeded in installing Arch. I installed it three times before understanding all the problems I encountered. However, I learnt a lot of things. As most of the installation is done manually, I was able to observe the different steps in the process. I also learnt how to connect to the internet thanks to commands line, to install xorg and a graphical environment.
First, I tried to keep the dual boot with windows but without success. I need to keep searching about grub to understand how to add windows to the loader. I still have my former windows partitions somewhere (over the rainbow…)