Is 'go' = 'gå' only if the going is done by walking? So if I go by car/train/plane I have to use a different verb?
When 'gå' refers to a persons movement, it means 'to walk'. (Except when it doesn't mean to walk)
You would say "I travel with" instead: "Jeg reiser med tog/fly" or "I drive with": "jeg kjører med bil".
Takk! Can 'åke' be used instead of 'kjöre'? Jeg kjörer til Oslo. Jeg åker til Oslo.
Neither 'åke' nor 'kjöre' would work in Norwegian. You should always use 'kjøre' in that context. (or 'kjoere' if ø is unavailable, but neither ö nor oe works as replacements in Duolingo afaik)
I've never heard anyone ever use the word 'åke' in Norway, so I wouldn't recommend you using that either. It's listed as a loanword from Swedish in my dictionary, but not with the meaning of 'drive'.
I do use the correct characters with exercises, since the special characters are displayed (and clickable) below the exercise, but obviously that is not the case with comments ;) My dictionary (from 1996) claims 'åke' to be driving, and then has a phrase 'åke inn' (to be sent to prison), so I'll just throw Åke away.