Recently I met the "pair programming" term, which refers to two developers working together in the same task. 
There are plenty ways for this to happen. The most common though is that a developer writes code, whereas  the other shares ideas.  

I have discussed with many developers that tend to be a sort of full stack developers and if you ask them about their position they reply that they are back-end developers. It seems that it exists an inexplicable reason of making the developers believe that back-end is 'harder' than the 'front-end' and of course the harder way, the better developer. (I am not fond of this idea).
Do what ever you want but be GOOD at it!