How to share a YouTube video with a specific start and end time

Sometimes we want to clarify an information sending a link to a youtube video, but we are only interested in a certain fragment, and we don't want to bore our receiver with the entire video.

First of all, we have to rewrite the video's URL, from this:
https://www.youtube.com/watch?v=o7a7ZAqWBIs
to this:
https://www.youtube.com/v/o7a7ZAqWBIs

The important part is the ID of the video, in our example: o7a7ZAqWBIs

Then, we can specify extra parameters to set the beginning and the end of the video, in seconds.

start=70, means 70 seconds from the beggining (i.e. 1:10),  and end=90 means 90 seconds from the beginning (i.e. 1:30)

https://www.youtube.com/v/o7a7ZAqWBIs&start=70&end=90

And finally the option to auto play the video:

https://www.youtube.com/v/o7a7ZAqWBIs&start=70&end=90&autoplay=1