Like other SHL published tests, both the situational judgement and the logical reasoning tests are positively scored for accuracy - which means that you can make an educated guess on any answers that you don't know.
The raw score (number of correct answers) will be measured against a norm group to create a percentile score. This score is used to determine whether you have performed well enough to move on to the next stage in the Microsoft recruitment process.
The passing score for the Microsoft aptitude test will depend on the role that you have applied for, so the best bet is to ensure that you have practiced and aim to get the highest mark you can.