If you have Westlaw or Lexis, you can enter the numerical portion of the citation in the search box at the top of either service. The same can be done on Google Scholar. If you do not have Westlaw or Lexis or access to Google Scholar, you can also find the citation in print.
If you have the citation for a case, go to the print reporter that would have that case. Say for example that your citation was Johnson v. Smith, 125 So.2d 1717. You need to first ascertain what the abbreviation stands for. There are many case reporters in print with different abbreviations. The reporters publish state and federal cases. In our particular example, the So.2d designation stands for the Southern Reporter second edition. The first number stands for the volume number and the second number stands for the page number. Based on this, the case you are looking for can be found in volume 125 of the Southern Reporter second edition. Once you have that volume in your hand, open it up to page 1717.