This sequence will be about the error-correcting capacity of a linear code. We describe the way of considering the space Fq^n as a metric space. This metric is necessary to justify the principle of decoding that is returning the nearest codeword to the received vector. The metric principle is based on the following concept: the Hamming distance between two vectors is the number of coordinates in which they differ. The Hamming weight of a vector is the number of non-zero coordinates. Here we give some examples. So, the Hamming distance between these two vectors is 2, since they have two coordinates in which they differ. The Hamming distance between these two strings is 1 because they just differ in one letter, and the Hamming weight of these vectors is 2 since it just has two elements which are non-zero. The Hamming dist