When malt whisky has completed its maturation in a bonded warehouse, it is ready for the final stage in the process, bottling. It's worth saying at this point that there can be - and often is - an intermediate stage, blending. Single malt Scotch whiskies have seen a resurgence in recent decades, but it remains the case that a lot of malt whisky is destined to be blended, either with other malts to become blended malt Scotch whisky, or with grain whiskies to become blended Scotch whisky.
The bottling of single malt Scotch whiskies usually takes place in industrial bottling plants far from the distilleries that produced them. This means that you will very rarely have the chance to see this part of the process during a distillery visit. Glenfiddich Distillery still has a large scale bottling plant on site, but while this used to form part of the distillery tours it offered, that is sadly no longer the case. Other distilleries with bottling facilities include Bruichladdich on Islay, and Springbank in Campbeltown. A number of smaller distilleries also do their own bottling.
When whisky is laid down to mature at the end of the distillation process it usually contains between 65% and 75% alcohol. Over the years of maturation (a legal minimum of three years, usually 10, 12 or more), some of the alcohol evaporates ("the angel's share") and by the time it is ready, the liquid in the cask will contain between 50% and 65% alcohol. Most single malt Scotch whisky is sold at a strength of between 40% and 45% alcohol. This is achieved by diluting the spirit as it is bottled, usually with distilled water, unless the whisky is being bottled at the distillery at which it was made, in which case the water supply used for the main distillation process may also be used for dilution. However, some whiskies are not diluted at all and are sold at "cask strength", i.e. they are bottled at the strength at which they emerge from the cask.
Finally it is worth noting that some distilleries "chill filter" their malt whiskies as part of the bottling process. This involves the whisky being chilled to around 0°C for single malt whiskies or -4°C for blends, and passed through a series of fine filters. The benefit of the process is a cosmetic one: it removes particles which might otherwise cause the whisky to become cloudy if chilled during serving (i.e. if ice is added). On the other hand, many believe that chill filtering can have an effect on taste, and some distilleries pride themselves in not chill filtering their whiskies. The phrase "non chill-filtered" is therefore quite commonly used on labels: it simply means that the contents of the bottle have not been through the chill filtering process.