Matlab filter design

Can anyone help me with Matlab filter designing? I have to import an analog sound file to matlab and then conver it to digital form. And then I have to send my signal through a low pass filter and then play back the sound and get the time domain graph.
I tried to do this for weeks through the help of ebooks and so on but I couldn't get the hang of it as IM new to matlab.
I would be really grateful if anyone could help me with this as soon as possible.
Thanx very much

did you check out the functions butter() and filter() ?

check this link out, **broken link removed**

Thanx very much.

thank you for the great link gregoost