When is the word "gehen" properly used? Is it only used to indicate walking?
For example, are any of these correct:
- ich gehe nach Moskau (if I live in, say, South America)
- ich gehe mit dem Flugzeug
- ich gehe zur Schule (if I have to drive)
Gehen as a motion to a place is basically either of the following 3:
1.: "to go some place by foot" / to walk
2.: "to go some place for a longer period of time"
Ich gehe für 2 Monate nach Japan.
Note that in this case your means of transportation are not of any interest.
3.: "to frequent a place"
Mein Sohn geht gerne zur Schule.
Ich gehe oft ins Fitnessstudio.
Also here the means of transportation are not of any interested. If you want to say something like "I go to the airport", you should use fahren if you go by car or public transportation. Gehen is only appropriate if you really walk there.
Example 1 is ok. 2 should be
Ich fliege mit dem Flugzeug.
because you fly as opposed to drive/ get driven or walk.
The third one is not ok if your focus is on HOW you get to school. If you drive you should say:
Ich fahre zur Schule.
"Ich gehe zur Schule" is only proper if you want to say either that you walk there or that you generally are going to school at the moment.
The first and the third are correct. The second isn't. You may say:
Ich nehme das Flugzeug.
The German word "gehen" has many meanings with only one being "walking". The Duden listes 15 different meanings (30 if you count the "sub meanings").
For example, it can also mean "to go", "to leave", "to function", "to visit regularly", "to dress up as", "to use something (without permission)", "to be with someone (romantically)", etc.
"Walking" is probably one of the less used meanings unless the speaker emphasizes the word or it's obvious from the context. For example, "Ich gehe den ganzen Weg nach Hause" would mean "I walk the whole way home."
If you expressly want to say you are walking, then you usually use the verb "laufen". This however opens a whole new can of worms, because depending on the context "laufen" can also mean "running". You'd use "gehen" again instead of "laufen" to express that someone is not running but walking. See: Was bedeutet eigentlich "laufen"?
This means that your examples can be interpreted differently depending on the context.
Ich gehe nach Moskau.
Usually means "I am going to Moskow", but if the speaker were (for example) at the airport the meaning can shift to "I am leaving for Moskow". If he wanted to say that he's walking he'd use "laufen".
Ich gehe mit dem Flugzeug.
As the others suggested this is wrong, and no one would say it, however if someone would say it, personally I'd interpret it as "I am leaving with the airplane".
Ich gehe zur Schule.
Here especially I would say it depends very strongly on the context. It can mean "I'm currently on the way to school", but also "I go to school (because I don't have a job and I'm still a student)". Only as an answer to "Wie kommst du zur Schule?" ("How to you get to school?") it would mean "I walk to school".