The CE C Software Development Kit incorporates a wide variety of tools and documentation in order to build programs in C natively for the TI-84 Plus CE / TI-83 Premium CE calculators series.
It is recommended that you grab the latest release from here if you are looking to get started. Feel free to also bookmark the wiki pages, as they will become quite helpful.
Included you will find examples using the 'Standard' CE C Libraries. These provide efficient and easy support for graphics, file I/O, keypad input, etc. Be sure to grab them if you plan to use them.
The header documentation will let you know about the available functions.
You can join us on the EFNet IRC server, on the #ez80-dev channel, if you have any questions (webchat link).
If you don't get a response in a reasonable amount of time, feel free to ask it here and we will get back to you as soon as possible.
If you want to contribute to the toolchain, feel free to open a Pull Request, or submit an issue/feature request.
If you would like to build the toolchain from scratch for your OS, visit the appropriate wiki page. Thanks!