BibTeX is a reference management tool to format reference lists and in-text citations to support a LaTeX document. Reference entries are stored in a plain text file in BibTeX format, which is external to a LaTeX document (.tex) with a file extension .bib.
In .bib file, each reference is formatted in a certain structure and is given a "Citation Key".
A BibTex reference entry consists of three main parts: 1. Entry type, 2. Citation Key, and 3. Field type.
1. Entry Type: Begins with @ symbol and followed by an entry type (e.g. Article, Book, conference...)
2. Citation Key: Unique name to identify a reference entry and is used to embed a specific reference entry in \cited{ } command to create a citation in a LaTeX document
3. Field Type: Includes bibliographical data about a reference
It is important to create an easy-to-remember and descriptive citation key. The most commonly-used pattern is to use last name of first author followed by year. 
Please be noted that not all bibliographic data is required (e.g. abstracts and notes), you may decide not to import them from EndNote or delete them from your BibTeX file.