You can specify a path to the input file if you want to, either absolute or relative to your current working directory, if it's in a different place. Naturally you'll want to use whatever filename you've chosen. Undoubtedly the data you're using is at least a vector and probably a matrix. Thus you'll need to know how to address the specific elements. This example presupposes that your input matrix is large enough to have a third row and second column.
Index exceeds matrix dimensions.
I used the size command to discover how big my matrix actually is. This command returns the rows and then the columns, so data is 6 by 2. This is the fastest way to get things done, both in terms of coding simplicity and in speed, a good portion of the time. You'll want to know how to access large contiguous chunks of your matrices. Without a designated step size the default is 1.