what is the difference between ''just then'' and ''just now'' ?
And should I add them at the beginning or end of a sentence?
example:
''Did you hear that sound just now?'' or ''Just now, did you hear that sound?''
''Was it you on the TV just then?'' or ''Just then, was it you on the TV?''
I don't know if the examples I gave are right, it'll be great if you can add some examples too :)

Question

what is the difference between ''just then'' and ''just now'' ?
And should I add them at the beginning or end of a sentence?
example:
''Did you hear that sound just now?'' or ''Just now, did you hear that sound?'' 
''Was it you on the TV just then?'' or ''Just then, was it you on the TV?''
I don't know if the examples I gave are right, it'll be great if you can add some examples too :)

Answer

Just then refers to something that has happened a few moments ago and may be about to happen again like a noise outside. Just now refers to something that happened a little while ago but is now finished.

Putting the words at the end of the sentence sounds more natural to me. "Did you here that noise just then?"

Answer

Just now is present tense and just then is past tense.