Know the two important modules in SAS code - the Data Step and Proc Step, and when they are used and for what purposes. In SAS programming, the source code is divided into two main modules: the data step and the proc step. The data step is a block of code that pertains to modifying a data set, such as its variables and observations, or transferring data from one place to another. The proc step is a block of code that performs an action with the data, such as printing, reporting, or sorting. A data step begins with the keyword "data" and ends with the keyword "run", while a proc step begins with the keyword "proc" and ends with the keyword "run".