Yoga instructions of all poses?

Could be interesting also for strength and cardio exercise! 

There is a big list without any description to understand what is it. 

Those are just general commonly used names, but you are in no way bound to use them exactly as defined. Use exercices you know, whether you use the exactly same names or not, is little important. But if you want to know the deifinition better, check the web. For example this website has a nice list of Yoga positions: https://www.yogajournal.com/pose-finder

you can't change the names

Yes, that's right. If you need to change the name of a position, you can pick any existing one, and add a note explaining what you intent to do instead. Notes are editable.

On my watch (Vivoactive 4) I only see the name, not the note. So unfortunately that doesn't work for me. 

OK, but what exactly are you asking? The list is not editable, so if you need to exercise some position (let's tell a "Dog"), and do not find it on the list, pick another one that you normally do not use, put the "Dog" into the comments, just for the record, that you do not forget it (regardless whether your watch shows it or not). When you then do the workout, and cannot remember the replacments, note it somewhere else, so that you can consult it. That's about all we can recommend you here.

It will be a better picture and name poses

I am asking what I asked in my first comment. Just if there's a page where I can see video's of all the poses. That's it. To learn and to create my own workout.

If I create a workout I would like to see the correct name on my watch, plus see the video there as welll. There are many different yoga poses, and one workout has maybe 50+ poses. Can't remember everything yet. Using another name and writing a note somewhere to remember what other name it should be, like you suggested, doesn't sound like a good option to me. With a pretty advanced watch and all the Garmin stuff available there should be a better way. 

With a pretty advanced watch and all the Garmin stuff available there should be a better way. 

Perhaps it should, and perhaps there indeed once will be a better way. In the meantime you can only use the options I proposed: you lookup the positions on the web, or you create your exercises to your likning and use the names that are available. Or you just wait till Garmin makes a video for each position.

They already have videos for each position. :) And they're scattered around their many workouts. Again, just looking for a place where I can check them all, instead of searching and clicking around for ages.