cores are lectures where the prof just speaks and you take notes. Generally tutorials are like reviews and discussions of what was covered in lectures. Labs are where you do hands-on stuff and usually take 2 hours or more.
Depending on your faculty most courses have either: 3 lectures only, 3 lectures 1 tutorial, 2 lectures 1 tutorial, 3 lectures 1 lab(often more then one hour long), or in sciences 3 lectures with 1 three hour tutorial and 1 three hour lab alternating every week.
Lectures are denoted as "C0x" where x is a number thats not important (e.g Econ 1B03 C01). Labs are denoted as "L0x" and tutorials are denoted as "T0x".