You may occasionally need to miss a class. The lecture notes online can not replace the interaction of being in class, but you may want to look at them to help you catch up.
Full Slides
These may be easier to view or for use to review any missed instruction.
Podcast or Video
When available, these will give you a quick summary of the lecture.
Slide Handouts
Use these to copy the notes from a classmate or set up problems.