The Inca Trail itself involves three full days of walking with a few hours to the Sun Gate on the fourth day. Your trekking group will be accompanied by a guide and assistant guide(s) for groups of eight or more. This means one is able to lead and another can stay behind with the slower members of the group, which means everyone can set their own pace. You'll find that the group you are trekking with will naturally spread out along the route but you'll all meet up again at lunch stops and at camp.
The trek follows varying terrain with challenging uphills, enjoyable flats and long downhills that can be hard on your knees. What this means is that some sections will be more difficult than others, especially getting to Dead Woman's Pass on day 2 of the trek. It's certainly not for the faint hearted but it's definitely not the same as tackling a mountain summit. Fear not as there will be ample rest stops to soak up the scenery and give your legs a quick break.
The key to enjoying the trek is to go slow and opt for small steps over long strides. Stay hydrated and take breathers as often as you need. Walking poles help massively and can be rented in Cusco at very low prices. Remember that it's not a race, focus on soaking in the spectacular scenery characteristic of unique experience.
You'll find lots more useful information about the Inca Trail trek on our tour Trip Notes which are available to download from the tour pages.