The IEEE is the Institute of Electrical and Electronics Engineers and their citation system is what they require of authors writing for their publications.
IEEE referencing is a numeric system that consists of a two part process:
Where does the number get entered?
Put your citation number directly after the reference, not at the end of the sentence (unless this is where the reference is mentioned). Punctuation should be placed outside of the brackets.
IEEE Style uses a notational method of referencing when referring to a source of information within the text of a document.
In its simplest form a citation is given in the text, consisting of a number enclosed by square brackets:
The full details of the source are given in a numerical reference list at the end of the document: