Understanding biostatistics is crucial for the estimation of sample size, determination of the power of the study, and assessing the statistical significance of the research outcome. In modern days, the estimation of the optimal sample size is a challenging and difficult task for the researchers. Although the inputs for sample size estimation for studies are predominantly available, the justification of sample numbers is still an enigma for many researchers. This chapter covers all the basic aspects of biostatistics and methods of sample size estimation in a manner that will infuse confidence in researchers and motivate them for effective calculation of sample size and to derive competent findings from their research data.