FIR Filter matlab command i'm trying to understand the fir1 filter but i still don't get it. For example here i got an audio signal that i consider noise, i'm passing it through a low pass filter. 

n = 100000
fs = 11025
handles.noise = wavrecord(n, fs, 'double');
nfilt = fir1(11,0.4); 
fnoise = filter(nfilt,1,handles.noise); 


Why did i need to pass the noise signal to a low pass filter in the first place? and why is the number of coefficients 11? also the 0.4 shouldn't it be a range of values?

I know these are a lot of questions but when i get to understand them, ill be grateful to everyones help.
Matlab FIR-1 command designs FIR filters with at least two given parameters. P1: The order of the filter, P2: cutoff frequency, assuming a default lowpass filter. Order of the filter N determines a number of properties of the resulting filter such as its comptational complexity, transition bandwidth, passband and stop band ripples. In general large N gives better (closer to ideal) frequency response but worse computational load. Also order of filter being even or odd will have effect on zero-locations being at Nyquist frequency which might be important for some applications with high/low pass filters...

The second parameter, cutoff frequency, is basicaly determined by the application.