Hi, mocallins. It's not complicated and shouldn't take 2 pages to describe:
If extension is for your use only:
1. Create a directory that represents system's root directory and call it anything you want--"rootdir" for example
2. In rootdir, put whatever directories and files you want to include in your extension
3. Open a terminal, cd to rootdir's parent directory, then: $ mksquashfs rootdir/ niftyapp.tcz
If you are going to submit the extension:
1. Create a working directory (call it niftyapp_project, for example) and inside of it put the following:
a. niftyapp.tcz (create as above)
b. niftyapp.tcz.dep (if applicable)
c. niftyapp.tcz.info
d. source code tarball and text file with compilation instructions (if applicable)
2. Open a terminal, cd to niftyapp_project, then:
a. $ submitqc
b. $ cd ..
c. $ tar -cvzf niftyapp.tar.gz niftyapp_project/
d. $ bcrypt niftyapp.tar.gz (when asked for an encryption password, use tinycore)
3. Email the resulting niftyapp.tar.gz.bfe as an attachment to tcesubmit@gmail.com (if no .dep file exists, mention it in the body of the email)
Don't hold your breath for a web interface. TCL is a self-help distro, like Arch Linux but even more so. You are expected to roll up your sleeves.