Starting from the theory, i wish to explain a full path to learn how to appreciate this sport:
I started without knowledge bases, a simple 10k after several years passed playing football. I ended in about 55′, good conditions.
The first thing to say is to decide what you want: a personal best or simply mantain a certain physical form.
The second goal is surely easier: 50km per week are enough. If you have never run it’s better start from 5-6km every other day, in a non-consecutive manner, that is alternating running fractions with walking ones. Increase the distance when the feeling is good and the workout is felt as easy.
When you are able to run 10km in 1h, your fitness level is decent, and you can simply mantain this level of fitness (maybe for you entire life…) or, going on reading and understand how the body works.

For running the weight is fundamental: before starting to have this kind of behavior, check to have a BMI below 25: an higher one means excessive joint wear.

In general, every person has an ideal weight range. Try to stand in the lighter blue band.
Hope the following articles can help you.

The basic of exercise physiology consist in Nutrition, Energy handling at microscopic level and Energy handling at macroscopic level.
Energy retrieval in human body

The applied exercise physiology is a good help for understanding how to improve the performance of human body: aerobic and strength training cover almost all the possible way of training.
Altitude, temperature and gravity have a deep impact on how the training. Diving sports deserve a speech apart.

Ordinary life
One of my best athlete is Nick Symmonds… reading the training log, i caught a lot of useful information about workload, during the week and during the year.
Body composition is both cause and effect of a performance, it’s possible to study the body of champion athletes on one side and overweight-obese persons in the opposite.
A moderate and regular physical activity is helpful for a successful aging.

I often find myself around the world repairing machine tools or trying to take some of them home to build.
Here’s how I do WU before the day:
Mulhouse, France
Torino, Italy
Caen, France