There is a lot of coaching information on the Internet, both good and bad. We have compiled a few relevant links below.
General training
First, the International Olympic Committee's athlete portal, where the amount of information you can find is staggering. You should log in as an athlete to get the latest updates and e.g. invitations to online seminars.
https://www.olympic.org/athlete365/
A slightly similar domestic site is Terve Urheilja. A lot of good stuff, although considerably narrower than the previous one.
You can also find a lot of useful information on SUEK's website. And of course https://puhtaastiparas.fi/ - online training is mandatory for national team groups.
Taekwondo
On the website of the Finnish Taekwondo Association you can find a lot of useful, if a bit difficult to find, things. The most important things for athletes and coaches can be found in the Enthusiasts menu, which is a bit confusing. You should check the news every week.
https://www.suomentaekwondoliitto.fi/
In particular, it is worth highlighting the material portfolio, where you can find a lot of material of varying levels.
https://www.suomentaekwondoliitto.fi/harrastajille/materiaalisalkku/julkaisut/
The history part is a tough thing.
https://www.suomentaekwondoliitto.fi/mita-on-taekwondo/historia/
A good package about history in English.
https://karate2sentena4.wordpress.com/2011/12/14/storming-the-fortress-a-history-of-taekwondo/
When looking at international fields, a good starting point is GMS, WT's international membership system. Here you can find international ranking competitions and value competitions as well as the current rankings of athletes.
https://worldtkd.simplycompete.com/
The website of the World Federation also has a lot of useful information, e.g. up-to-date rules.
http://www.worldtaekwondo.org/
The website of the European continental confederation also has necessary information, especially about the European Games.
https://www.worldtaekwondoeurope.org/
If you want to explore the careers of different athletes, the best address is Taekwondodata. The site is a good starting point for opposition analysis in international tournaments.
https://www.taekwondodata.com/
There are few news sites about the sport, but at least MasTaekwondo is worth following.
Inside the Games also produces interesting material.
https://www.insidethegames.biz/sports/summer/taekwondo
Actual coaching knowledge is scarce. Especially in Finnish, the offer is really thin. Kim Sinisalo's blog is an absolute source of information. In particular, it is worth highlighting 4 blog posts that everyone interested in the sport should read.
http://ventrikkeli.blogspot.fi/2012/03/alyn-ja-luovuuden-renessanssi.html
http://ventrikkeli.blogspot.fi/2012/04/painavan-kivijalan-tie.html
http://ventrikkeli.blogspot.fi/2012/06/tekniikan-maailma.html
http://ventrikkeli.blogspot.fi/2013/10/taekwondon-pelivalmennus-yleisesittely.html
Finally, let's raise our club's own tail a little and recommend Teemu Heino's blog, where various aspects of the sport are discussed in well-thought-out writings. The pace of publication is calm, but the content is even tougher.
Happy reading moments!