You should choose a parametric test if your data is sampled from a population that follows a normal distribution (or Gaussian distribution). The normal distribution is a pattern for the distribution of a set of data, which follows a bell shaped curve. This means that the data has less of a tendency to produce unusually extreme values, compared to some other distributions.
Descriptive statistics: numerical summaries of samples (what was observed);
Inferential statistics: from samples of populations (what could have been or will be observed).