tce-fetch is not recommended as it does not check md5 sums nor handle dependencies and requires 'sudo'.
$ tce-load appname.tce wget install
Handles md5 checking and dependencies, downloads and 'installs' the named extension as using appbrowser would do.
$ tce-load appname.tce wget
This will handle md5 checking and dependencies and downloads. This is like using appbrowser "Download Only"
If using command line tools, be sure that you are storing the extensions into a proper "tce" directory or you will experience much grief.