Newbie addon question

[GI44]

I know this is really a basic question but I have never used any of the MODS/ADD ONS Can someone please explain how ADDONS and MODS work?

Do the ADDONS/MODS simply change some of the visual appearance of missions that you get with OFP OR
do they actually give you new missions?

For example, I saw a post for a MOD that provides winter scenery.  Does that just change the existing missions to be in the snow but the mission itself is unchanged from a game play point of view.  In other words, the same scripted triggers occur, the same goals, etc.  just the scenery is different?

Example 2:  If someone makes a mod that introduces guard dogs - what does that mean?  Do dogs just randomly appear in the missions you purchased from OFP or are they entirely new missions?

Sorry for the dumb question but I really don't know...

Thanks
GI44

[Major Fubar]

No, unless addons come with missions, all they do is add new units into the game engine.
You will never see these units unless someone releases a mission or campaign that uses them, or unless you go into the OFP Mission Editor and play around with them yourself.

[USMC Sniper]

No, they do not modify anything, just add new thigns to be used in your own/custom missions, or just for fun.