The courses that you need to include in your Personal Study Plan can be chosen from all the courses listed in the curriculum of your degree programme. Please note that some compulsory courses may have prerequisites (courses which  have to be taken before others). This means that you cannot add certain courses to your APSP without including the pre-requisites first. 
The prerequisites are listed in the curriculum of your degree programme. Make sure you read it before you make your APSP. 

You can add new courses (belonging to the next academic years) to your APSP,  only after having included all your courses belonging to previous years.

You are allowed to take your third-year optional course (Free choice credits - Year 3) during your second year.
In any case, the system prevents you from making an irregular APSP in which the prerequisites are not respected. A  warning message tells you which courses must be included before others.