First part:
PHP is an open source object-oreinted scripting language. Essentially it is the main language used on *nix based servers. Though I am pretty sure it can also be used on MS IIS servers but I am not sure.
ASP is the Microsoft scripting language. It is native to the IIS web server, though I think there is a module for Apache that is able to utilize ASP.
Further explanation on details would take a lot of time and someone better than me.
For learning graphical design, I would suggest that rather than work on tutorials and such, look around for articles on design theory. Understanding the reasons "why" a layout works and looks good is much more useful than just being able to create one. For overall web theory
A List Apart: A List Apart has some very nice articles. Look through their archives.
Despite this, it is also very important to continue working on graphical skills. Personally I try to create one full work, from start to finish, every week. Not necessarily a full website or huge render. Some projects are very small and some are larger, dependent on the amount of time I have. Also try using different manipulations tool, and tolls that you do not commonly use. And as a generic tip to graphic design, I would strongly suggest to not attempt to create an entire work in one sitting. Consistently working for long hours will develop habituation and you will most likely start missing pieces of your work. You need the breaks to keep the project fresh.
Anyway, best of luck.