Here is how to properly format your citations and references

Citing your references in the text of your article

...a recent study (Esteban et al, 2004) showed... (When 3 or more authors)

...a recent study (Esteban and Buller, 2005) showed...(When 2 authors)

...a recent study (Esteban, 2007) showed... (When 1 author)

you could also say:

...a recent study by Esteban and Esteban (2007) showed ....

You should have a references section at the end of your article

These should be in alphabetical order in this format:

Esteban DJ.  An interesting biological study. Journal of Interesting Biology. 2007. 72(3):356-370.

Esteban DJ, and Buller RML. Ectromelia virus: the causative agent of mousepox. Journal of General Virology. 2005. 86(10):2645-59.

Esteban DJ, Nuara AA and Buller RML. Interleukin-18 and glycosaminoglycan binding by a protein encoded by Variola virus. Journal of General Virology. 2004. 85(5): 1291-1299.