citation is all about citing where you got some information. it's that simple
imagine you're writing a paper about marketing theories. you'll probably have to write about existing theories, new findings, research in that field.
let's say that you mention maslows heirachy of needs in your paper to build an argument. you should cite the original paper or the source you've taken that information.
same goes for any other data you've noted in your paper. if you've mentioned sales data you should cite where you got them from
the whole idea behind citing in academia is to ensure the readers can find the sources if they need further elaboration. this is the reason why a research paper would list 10s or even more than 100 other papers.
there are many different styles like harvard, apa, chicago, ieee etc. you have to adhere to the style the university asks you to use
btw get a reference manager software. I'd recommend mendeley
never ever do the citing manually!!!.
always use a reference manager. this way the references can be generated automatically without you manually having to list them
https://www.mendeley.com/reference-management/reference-manager
good luck
දන්න එකෙක් ඇවිත් කියයි..
...ada eki endan aave udai pallehai kali dekak witarai...Meda hariye ekiwwe bada hariye full open 
... ekigen citation igena ganna thibba nam...maru 
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