How to learn embedded C?

You can't "download the development tool" for "embedded C" because it isn't one tool: it's a compiler / linker / library package for the specific processor (or processor family) that you want to develop for. And the package for an embedded PIC processor will not work with a Z80 based system, which would be useless for an ARM device, and that wouldn't work for a ... you get the idea.

To develop embedded software, you need the processor, a board it will run in (preferably the device you are trying to produce) and the development environment for that specific processor (and you may need others for other chips as and when: FPGA's for example need their own systems. You will also need the correct cabling to connect your computer to the device in order to get your program into it for testing.

By the way, do not expect the same level of help and assistance you get for VS development: debugging systems are likely to be basic at best, and "up to you" at worst. Embedded dev is not for the inexperienced developer, it's very different from the PC world where all the low level stuff is done for you ... Heck of a lot of fun when you are used to it though!

Arduino and the following book are your best bet for learning this:
AVR Programming: Learning to Write Software for Hardware (Make: Technology on Your Time): Elliot Williams: 9781449355784: Amazon.com: Books[^]
I mention this book because it takes you one step further down toward the metal (using C and AVR GCC) instead of Arduino dev environment.

It's a great book and helps connect the h/w to the s/w of embedded programming.