"I am beginning."
Because that construction does not exist in German.
Have another look at the tips and notes for the very first unit: https://www.duolingo.com/skill/de/Basics-1 -- in particular, the section on "No continuous aspect".
The tips and notes are unfortunately not present in the mobile apps yet, but only on the website -- and you may need to use a PC or tablet to read them as the website has been known to act like the mobile app (including hiding tips and notes) when viewed on a small screen, as with a smartphone. Requesting the desktop version and/or using a different browser may or may not work in this case.
I recommend always reading the tips and notes before starting a new lesson.