Basic Fourier Series Not Understanding how to interpret n values
I'm assuming the "n" you are referring to is the coefficient index, also referred to as the harmonic number; i.e. the n=3 term refers to the "third harmonic". 

The n=0 term is the average value of the function, and is sometimes called the "DC component" because it does not depend on time. 

Depending on the version of the Fourier series you are using, the terms in the series could go from negative infinity to positive infinity, or they could just go from n = 0 to positive infinity. The trigonometric version of the Fourier series (with sine and cosine) starts at n=0 and goes to infinity, whereas the complex exponential version (i.e. $c_n e^{j\omega_0 n t}$) has terms for negative and positive values of n. 

The two versions are equivalent because the negative n terms cancel out the imaginary parts of the positive n terms in the complex exponential series.