The trek is simply a walking route. In nepal most of the walking routes that we, as tourists, use in our treks, are actually the "roads" of the Nepali people that live in the mountains. This "roads" are of course just paths, usually carrying people and donkeys, but - it won't take long until those paths will turn into real roads, carrying real motor-vehicles.
That's why you should go for a trek in Nepal as soon as possible, because the progress in some areas is really dramatic, therefore some places won't be so unique as they are today.
So- there are no motor vehicles in the trek, that's why you won't hear a single motor noise even if you try hard, there is no polution, and the air is so clean you actually wonder if it really exists.
The touristic treks, such as the Annapurna sancuary and Around Annapurna , go through paths and trails that connect villages along the route. That's why the trek takes you to amazing landscapes, but still don't leave you for days with no place to eat and sleep. You will always find villages on the way, usually containing one or more guest-houses that will be happy to give you a place to sleep and usually a really good food to eat.
The trek can take few days or few weeks, it all depends on your mood, strength and will.
You set the pace - you can walk 15 kilometers a day or just four kilometers a day, and spend the night in the village you reach on the way.
Another advantage of going through inhabited places is that you also meet the local Nepalies.
You'll see them working in their fields, learn about amazing irrigating technics, walk with the children on their way to their schools - sometimes so far as a walking day you'll walk, and enjoy their lovely hospitality at night.
The starting and ending points of the touristic treks can be accessed usually by car, bus, or plane.