The LEGNTH Statement (before the SET) allows you to define the length of some/all of the variables, and will permanently reset the length in your PDV and data set Iif you rearrange the variables in this LENGTH statement, it will also re-order your variables!). If you put the LENGTH statement after the set statement, it will not change the length in the PDV.
The ATTRIB ("attributes") assigns many items to each variable assigned, such as Format, informat, length, Label, and transcode(Y/N).
Here are links to helpful SAS documentation: Attrib Statement
Length Statement