What are in-text citations refrences?

im doing a essay regarding a promp that my teacher gave us and she wants for us to include IN-TEXT CITATIONS REFRENCES, what is this , hoe do use it in my essay do i have to include this while writing my essay or or just created on sheet of paper and attach it to my essay does the in-tex citations refrences go after a sentence , does it have to be capitalized ? please give me all detail