when you line up, are you on line or in line?
Q1:when you want people to line up straight and want to ask them to go at the end of the line to line up, which sentence below is correct?
(I want to use 'back' instead of 'end'.)
1)please go to the back.
2)please go at the back.
3)please go in the back.

Q2:what is the opposit word of back in this case? if it is 'front' which one is correct?
1)go up front.
2)go to the front.
3)go at the front.
4)go in the front?

Q3: when you are queuing, are you on line or in line?I would appreciate if I could get more answers or opinions from any of you. thank you in advance.

Question

when you line up, are you on line or in line?
Q1:when you want people to line up straight and want to ask them to go at the end of the line to line up, which sentence below is correct?
(I want to use 'back' instead of 'end'.)
1)please go to the back.
2)please go at the back.
3)please go in the back.

Q2:what is the opposit word of back in this case? if it is 'front' which one is correct?
1)go up front.
2)go to the front.
3)go at the front.
4)go in the front?

Q3: when you are queuing, are you on line or in line?I would appreciate if I could get more answers or opinions from any of you. thank you in advance.

Answer

Q1 please go to the back (of the line)
Q2 go to the front(or head) of the line
Q3 I use "in line", but I've heard "on line", particularly from New Yorkers.

Answer

thank you for the answer, Hilary!
nice to hear you are learning Japanese!:)

Answer

Hi Chemmie -
1)  please go to the back
2) go to the front
3) in line 
Note that British English speakers would be more likely to say go to the back of the queue - we use line too, but queue is also very common.  I have never heard a British English speaker use anything other than 'in line' in this context.  "Online" only has meaning for us in relation to being on the internet.  BTW, I live in Australia, but grew up in England.  I am also learning Japanese!