Designing A Filter Using SPTool In Matlab
John Smith, 

You are designing a low pass filter, which means that your filter will be applied, (convolved) against a signal, whereby it will attenuate certain frequencies, and leave other frequencies more or less untouched. 

So in a low pass filter, generally that means that you will filter out (heavily attenuate) frequencies that are 'high'. Your $f_{pass}$ just quantifies this for you. How high is high? Well, if you want a 'cutoff' at 200 Hz, then that generally means you want to keep frequencies at roughly 200 Hz and below, so pick $f_{pass}$ to be 200 Hz. 

But bear in mind, you usually have a specification about transition bandwidth. If your filter is infinitely sharp, you can say that you accept all frequencies less than 200, and attenuate all frequencies above 200. Realistically however you might want to accept all frequencies less than say, 130, and then from 130 to 200 you are transitioning, and then heavily attentuate all frequencies greater than 200. 

Regarding the sampling rate, that is really dependent on your simulation. If you pick 10,000 Hz as your sampling rate, then you should make sure that when you use your filter on a signal, that it too was sampled at 10,000 Hz. 

It is good that you are using MATLAB. It is a very powerful tool in understanding DSP concepts.