When it comes to front end, back end and full stack developer, the difference is determined by :
front end (the visible parts of a website)
back end (the “under the hood” databases and infrastructure)
full stack (a hybrid of both)
And front end developers work on technologies that are used to build front end(which is what clients visiting that website see)of application like HTML,CSS, Javascript ( Node js, Angular are also now used ).
Similarly back end developers work on back end technologies like Node js.
Full stack developers work on both front end and back end developers and know both end technologies as well.
For example :
MEAN Stack developer where
M stands for Mongoose ( Back end database technology )
E stands for Express ( Back end technology)
A stands for angular ( front end technology)
N stands for Node ( back end technology)