I'm no expert on photography etc and there will be far more complete answers than this, but yes you need to compress.
First thing to remember... don't alter or compress the original pictures "on the memory card" if you intend keeping them or using them for making high quality prints from. If you do the original quality is lost and the camera also won't recognise the picture anymore.
Move the picture/s across to your PC (drag and drop or right click and "send to"). You then have a picture to play around with leaving the original intact. If you want to archive and keep pictures AND compress as well to email, then when you have moved them to your PC simply make a copy that you can then edit etc.
Compressing pictures... if you hover your cursor over a picture or open it it will say somewhere the file size eg 3.5mb. That's to big for normal email, you want around 80 to 200kb for each picture. That keeps reasonable detail.
If you have "Paint" installed on your PC... which come as standard with Windows Vista (I'm guessing same with W7 too) then right click a picture, move to "open with" and paint should appear. A big image of the picture will open.
Select "image" from the toolbar on the top, and there is an option to "resize" in percent. Chnage horizontal and vertical to (say) 30% and save the picture... a bit of guesswork and hopefully it's at a more manageable size, just nicely fitting your screen. If it's way to small or still to big just use "edit" on the top toolbar and "undo" and try a different percentage.
As mentioned there are dedicated programs to all of this, paint is basic, but works well.
As for videos...think you will need 3rd party software for that.