If you know about such equation as:
mx'' + cx' + kx = F
Then damping is c <img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" />.
When something flies, it loses its speed because of flying in air. Let's say "linear damping" is a force with which air reacts on flying object. It is theoretically proportional to object's speed.
There are so many interesting things to talk about in 'learn' section that is hard to choose. Actually I think those would be very helpful:
<img src="{SMILIES_PATH}/icon_arrow.gif" alt=":arrow:" title="Arrow" /> how does the quantity of for example speed or acceleration influence on object's real speed measured in pixels per second? (you know what I'm thinking about?)
<img src="{SMILIES_PATH}/icon_arrow.gif" alt=":arrow:" title="Arrow" /> how does "effects" work (some images showing for example two shapes overlapping each other and one of them or both were given a special effect from the list)
<img src="{SMILIES_PATH}/icon_arrow.gif" alt=":arrow:" title="Arrow" /> simple .cap that'll show usage of every movement and how to adjust parameters to get interesting effect (for example using bullet movement for bullets but also for walking enemies as well)
<img src="{SMILIES_PATH}/icon_arrow.gif" alt=":arrow:" title="Arrow" /> articles showing some practical aspects when making any game... like: "how to store variables like score, ammo etc."
Well, there could be more articles in 'learning' about:
<img src="{SMILIES_PATH}/icon_arrow.gif" alt=":arrow:" title="Arrow" /> how to make your own animation system
<img src="{SMILIES_PATH}/icon_arrow.gif" alt=":arrow:" title="Arrow" /> how to avoid bugs <img src="{SMILIES_PATH}/icon_wink.gif" alt=";)" title="Wink" />
But sure they'll be obsolete too fast too even care about making some <img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" />.