Understanding the graph on lab 2

The colors of the graph may vary, depending on which spreadsheet program you use.   'Dots' show on libre office and excel, where the the digitization occurs on the signal.    But, this is the same as the leftmost point of the horizontal section of the square (or step) wave.

Notice the square wave also looks like a stairs or steps ...

I will assume you are using google docs, and you can load the spreadsheet fine (sampling.xlxs).   The 'I dont know where to begin' is a bit vague, because it may be various reasons why you are having difficulty.   

From these assumptions:

In short, the curve is the signal you are digitizing.   In libre office, the curve is red.    In google docs/excel, the curve is blue.     The digitized version (ADC, or step/square wave) of the signal, is in red for excel/google docs, but yellow in libre office.    The color is not important.   You should see 2 wave forms, one smooth, like a sine wave (the signal to be sampled), and a square/step wave (the ADC or digitized version of it).

Underneath the this graph is text, it says:

If you are using google docs, there is a small chance you wont see this, because the graph is too big and is covering it up.   Resize the bottom part of the graph, upward (click on it, and look for the vertical arrow at the bottom of the graph).    When you can see the text (above), you are good to go.

Now, this graph has 2 parameters.  What frequency for the signal (curvy wave), and  the sampling rate (in samples per second).  

Where (in the top green box) it shows 50, that is your signal (in hertz).   Change it to 500 for the lab.

Below it, is the sampling rate, in samples per second (how many times we scan it in a single second).   The lab will ask for various values: 500, 1000, and 950 (off the top of my head).    You will notice the blue wave remains constant (we do not change it, once we set it), but the digitized wave will change.

This wave is the digital approximation of the signal, based upon the values entered!

Let me know if you have additional questions.