In text citations are the citations that happen in the body of your paper. Within IEEE they are numbers within brackets which will correspond too the appropriate citation within the reference section at the end of your research paper.
In-text citations start at [1] and ascend in order of citations listed. Occasionally, you will reference a source multiple times in your paper, you can use the same bracketed number for each citation.
Here are some examples of in-text IEEE citations:
Single author
There has been at least 532 volcanic eruptions in recorded history [1].
Ramos [1] found 532 volcanic eruptions in recorded history.
Two different authors cited
There has been at least 532 volcanic eruptions in recorded history [1], [2].
Ramos [1] and Wilson [4] each found 532 volcanic eruptions in recorded history.
More than three authors on one single study
Ramos et al. [1] found 532 volcanic eruptions in recorded history.