Inside a sentence, か functions as an alternative marker.
※Behind a sentence, か functions as a question or emphasis maker.  Click here to see a sentence-final particle ka (か) page.
 

• noun1 + か + noun2 + positive = either noun1 or noun2　
あしたかあさって行きます。I'll go either tomorrow or the day after.
 
• Question word + か = some-  any-
だれかいませんか。Is anyone around?
なにか言ってください。Please say something.
いつか来てください。Please come sometime.
どこかへ行きたいですね。Don't you feel like going somewhere?
どれか決めてください。Please decide which one (you want).
 

 
• noun / verb-plain / い-adjective / plain + か + noun / verb-plain / adjective-plain / どう + か = whether . . . or . . . /not
来年かさ来年かわかりません。
I don't know if it will be next year or the year after.
来る(の)か来ない(の)か聞いていません。I haven't heard whether he is coming or not.
高い(の)かどうか知りません。I don't know if it is expensive.
食べる(の)か話す(の)かどっちかにしてください。Please either eat or talk.
 
※Basically, の nominalizes the adjective/verb in front of it.  It often disappears before か.

※な-adjective always takes the の before か.

ボロボロなのか、立派なのか知りたい。
I would like to know whether it is dilapidated or in good condition.
 
• sentence + か + と聞く = ask if . . . is . . .
試験は明日ですかときいた。He asked if the test is tomorrow.
試験は明日(なの) かときいた。He asked if the test is tomorrow.
 
• noun + なの / verb-plain / adjective-plain + か = possibly because
病気なのか、顔色が悪い。Possibly because she is ill, she looks pale.
聞こえなかったのか、返事をしなかった。
Possibly because he did not hear me; he didn't answer.
古いのか、味が悪かった。Possibly because it was old, it tasted bad.