Use 1 recording of 3 /a:/ made by a patient with Huntington's disease, find the file here.
Record 3 similar extended /a:/ of your own voice to compare results to.
Read first about simulation of jitter and shimmer and then study Praat's tutorial on Voice (i.e. including the links in the tutorial).
A good idea is to first read the instructions (for the whole practical).
Send the report to your teacher including pictures and reflections. Hopefully the literature has been useful and you can refer to it in your report.