Ctrl + Alt + T opens a new Chrome tab with the crosh shell (command line interface).
Fig. Chrome window with crosh tab
The crosh shell presents itself as a black window with a welcome greeting.
The last line shows a yellow input prompt (crosh>) with a red cursor behind it. If you enter help, you will get a really short list of commands.
top shows a list of started processes. Use the q key to exit the interactive view. I think the Chrome task manager, which can be opened with 🔍 + Esc is far less confusing, since it does not list all the system processes.
help_advanced shows a long list of commands, which are mainly used for system analysis. Occasionally, I use battery_test to check the condition of the battery. Some of the listed commands are not available on all Chromebook models.