Ascience begins working by trying to explain a natural occurrence that is

Naturalistic Observation
A scientist begins working by trying to explain a natural occurrence that is through naturalistic observation study. 

The two methods scientists use to obtain empirical or evidential data is through:
  
1. Experimentation. NATURAL AND LABORATORY. This will majorly utilized in the various fields of science, hence this uses the variables of determining the independent and dependent variables –causation and effect of one or two variables to one another and vice versa. This is widely done in laboratories but natural observations is also one condition.  
- naturalistic observation
- controlled setting

2.    Descriptive. This is one method of gathering data by using tests, interview and assessment, also to correlate the study. Moreover, this is the methods which is widely used in social sciences. Note that questionnaires aren’t the only methods in gathering data as mentioned by the above respondent, many authors would argue and support this claim.

Because a model would make the investigation easier to understand