What: LaTeX is a software system for document preparation, especially used as an editor for scientific documents while it makes easy to typeset complex mathematical formulas.
Where: There are many LaTeX editors freely available on the internet, one of which, Overleaf (used to be called ShareLaTex), is a widely used because it is a collaborative cloud-based version.
How: You type the content (with LaTex commands) into a LaTeX editor's document - any document created by LaTex editor ending with file extension .tex - then LaTex system can compile the source code in the .tex document, and finally generate a PDF file. In a sense of its finished product, the LaTex system is acts like MS-Word, but with the help of LaTex coding.
Why with BibTeX: Within a LaTeX .tex document, through the use of a package called BibTex, you can automatically generate and format a bibliography (the reference list) in the chosen style.
BibTeX stands for a file format - with file extension of .bib - that contains a bibliography or a list of references.
As an external, flat-file database, this BibTex file can be initially generated and transitorily stored within the Zotero or EndNote software program;
A BibTex file can be viewed as "transitory" as, in the end, the file would be uploaded / imported into a LaTeX editor program. In conjunction within a LaTex coding document (a .tex document), it makes possible that the cited works and references within the BibTex file appear in the output of your desire.
BibTeX is a bibliographic tool that can interact with LaTeX in organizing in-text citations and creating a bibliography.
Due to BibTex, each reference in the bibliography file is automatically formatted with a certain structure and is given a "key" (key = unique identifier of a bibliographic entry) by which you can refer to in a LaTex .tex file.
BibTeX interacts with LaTeX in a way allowing you to cite any reference that is contained within the .bib file. For detailed info on how to use .bib file within a .tex document, please see the box titled "BibTeX-related Commands" in the page "BibTex: What and How."
Video: What is LaTeX
Video: LaTeX Tutorial pt 1 - Creating Your First Document