More reading - this time about bottle conditioning. If my yeast attenuation level is say 80%, does that mean there would be enough sugars in the bottle for the yeast to carb the beer? Or would priming sugar still need to be added... Thanks in advance!
You will need to add priming sugar if the beer has reached its terminal gravity with the yeast being used.
In this example, despite the 80% attenuation the remaining 20% is not usually fermentable sugars. Its comprised of protein, dextrans and other molecules in solution that are largely ignored by your primary yeast strain.
Lastly, reported attenuation stats for a given strain are not a promise of performance. Wort composition (influenced by ingredients and mash conditions) will generally dictate the amount of attenuation possible of a given wort. It is possible to transfer a fermenting beer to the bottling phase prematurely, counting on the remaining fermentation to carbonate the beer. Generally, this is a difficult thing for most homebrewers to predict accurately enough and get reliable levels of carbonation.
The best way is indeed to wait until the fermentation is completely over. When you measure the same (low) gravity for 2-3 days in a row this is the case. The also allows for the yeast to clean up the by-products.
The bottom of your fermentation vessel will have a bottom of yeast, but normally there is still (much more than) enough yeast in suspension to make the bottle conditioning. You just have to calculate the priming sugar quantity with an online calculator (like this one: http://www.aussiehomebrewing.com/AlcoholChart/PrimingCalculator.html) or use sugar drops in the bottles.
Hope this was helpful.