I just bought a personnal license of Construct 2 but I don't know how to use it....
When I click on DOWNLOAD, it only dowload a text file "c2license.txt"
What I am supposed to do now ????
This is covered in THIS section of the Manual, specifically the part with the heading "The license file: c2license.txt".
Basically either place it in the C2 installation directory, or put it anywhere and use the 'About' box and just browse to it's location to select the license using the 'Load license file' icon.