Ok. It now worked. There were spaces. I copy-pasted the commands from the 1st post which contained spaces
I don't understand what to do here, he opens a black window but waits for the command. What do I need to enter there?
The description says what you need to write...
$ ant extensions
bash: ant: command not found
You have not installed ant.
You have not completed step 5 or 7. All steps must be followed carefully.