I want to learn VHDL but I really don't know from where to start.
I want some advice and explanation about the software I need to get started.
I would like also to get some references in order to learn it efficiently without wasting time by searching on the Internet, since there are a lot of e-books and tutorials and I'm really confused about which one to choose.
I suggest, you have good background in Digital Design. If not, start with any edition of "Digital Design" book or, alternatively "Contemporary logic design".
Download GHDL (VHDL compiler/simulator using GCC technology) or a little more friendly software tool boot.
Learn how to build a VHDL program with GHDL. Try to compile simple "Hello, world!".