Simple and Stratified Random Sampling:

Simple Random Sampling  is  a type  of probability sampling that ensure that each  element of the population has  an  equal and independent chance of being chosen. The  first step is to  identify the accessible population and enumerate or  list all  the  elements of the population. This listing is called sampling frame. After sampling frame  is  developed, a method must  be  selected to  choose the sample. Table of random number includes a  list of numbers that have  been generated  in  such a way that  there  is no  order or sequencing of the number. Today  these tables  are generated through the use of computers: 

Stratified Random  Sampling: Ther'e are many different characteristics that may  call  for the use  of  stratified sampling. It  is a type of random sampling in which  the population  is  first divided into two  or more strata or subgroups, before  sampling process begins. Each unit is assigned to  one  stratum based  on prior knowledge about  the unit. Then, independent random samples are selected from  each stratum using a procedure which  is used  in  simple random sampling. Stratum (plural "siratan) constitutes a portion of the population  i.e.  they  are mutually exclusive and collectively exhaustive. The sampling units of stratum are  similar in  each other and  the different from the members of another stratum in the characteristics that we  are measuring.