The partitions need to be mounted somewhere for you to be able to access to them. If they're showing up in df then they must be mounted, so look on the far right column of the df output to see what directory they're mounted on.
For example, here's on of my systems:
/dev/hda7 28209532 10437636 16338900 39% /
/dev/hda1 28898080 6661280 20768864 25% /home
/dev/hdb1 115377640 87424512 22092216 80% /home/share/backup
/dev/hdc1 240362656 169530520 58622336 75% /home/share/media
There you can see that /dev/hda1 is mounted as /home.