it depends on the type of software. if the software is able to use multiple cores, you will see more cores in use. if the software uses only one core, then you'll see only one core in use.
task manager shows all 8 logical cores. you're still using one processor.
you can force the programs to use other cores than the ones they're usually assigned by the os. from task manager, right click on any process in the process tab, select set affinity and you can set that process to run at the manually assigned core.
then whats the point to having quad core with hyperthreading?
hyperthreading lets the cpu to split it's core into two logical cores when workload demands it. if the software is optimized for hyperthreading, it can use ht to work better.
a lot of tasks such as video editing, rendering, encrypting benefit a lot from multiple cores and hyperthreading.