^ in da future i hope to do medicine or even engineering
Well depending on the type of Engineering you'd have to pick a particular stream (ie major) pretty early
For example if you wanna pursue a Master of Engineering (Civil) after you finish you have to the Civil Sytems major (
http://www.ssc.science.unimelb.edu.au/courseinfo/majors/new/civsys)
The rest of the Engineering streams can be found in the page Edmund linked.
Also to go on to Medicine you'll have to complete certain second year subjects (one each of anatomy, physiology & biochemistry) as prerequisites. 
The full approved list is here: 
http://www.medicine.unimelb.edu.au/docs/MDPrerequisitesVic.pdfI'm not sure if you can fulfil requirements for both MEng and Doctor of Medicine. Might have to call UoM.
and could u explain wat is breath subjects (i dont know muh about that)
Breadth subjects are part of the new Melbourne Model. You have to take 75 points in a 3 year degree. This basically translates to 1 per semester. 
Ie if you're doing a Bachelor of Science, you must take a subject each semester from a school other than science and eng