The first noble truth is that the existence is inevitably dukka or usually this is translated as suffering but that doesn’t encompass the entire meaning of this word. It means unsatisfactory, I think what the Buddha really meant by this word is that because everything is temporary, we are not able to satisfy anything into a permanent state and because of this we suffer and that it is unavoidable due to there being existence – this is just one aspect of dukka that the Buddha meant and I think one of the more important aspects of dukka.
The first kind of dukka is pain, both physical and mental pain – whether we like it or not, pain is an unavoidable part of our lives. Many cases to avoid pain actually increases it as with the case of a toothache that is put of for a few months and then when going to the dentist you experience more pain from having to have the tooth removed.
The second form of dukka is change we suffer because we think that our unhappiness, doubts, worries and negative emotions are permanent states and define who we are. But we should always appreciate this basic notion that nothing is permanent – everything is in everlasting change because anything that is made up of something (and everything is made up of parts) it is subject to change because those parts are inevitably broken down or built up into other things which make up a whole. This is because in existence everything is made from parts. Even the most basic thing an atom goes into making something and so when atoms make up wood – can you really call all those atoms wood? Or can you call wood just a bunch of atoms? Labels for different interdependent parts seems to define existence in a way. I guess the point I’m making is that because things are made from interdependent parts, they will always be subject to change because they are either broken down or reused and turned into something else.
This is thus what defines existence, the fact that all things are essentially just made up of other smaller things and due to this its law that because everything is made up of interdependent parts they will either decay and be broken down or they will be put to use and turned into something else (as is the case with atoms) and so nothing is complete in of itself because nothing can be unconditioned in terms of being free from the parts that make it and being free of being able to be built into something. Therefore because of this basic principle everything that will ever exist and can possibly exist is bound by the law of change. Or as the Buddha put it everything is impermanent.
The third and final form of dukka is one which requires serious contemplation and that is that if your existence if in being, then you must inevitably pass out of existence. This is something which I still don’t fully actually understand to be honest.
As always put my words to the test and see the truth for yourself.
Of course I am very new to Buddhism so take what I say with a pinch of salt and there are other resources listed below which may help you understand Buddhism a little better.
Buddhism Plain and Simple by Steve Hagen https://www.amazon.co.uk/Buddhism-Plain-Simple-Arkana-Steve/dp/0140195963/ref=sr_1_5?crid=34M92RA2NH4SR&keywords=buddhism&qid=1649083246&sprefix=buddhism%2Caps%2C79&sr=8-5\
Unhindered: A mindful path through the Five Hindrances by Gill Fronsdal https://www.amazon.co.uk/Unhindered-Mindful-Path-Through-Hindrances/dp/0989833402/ref=sr_1_1?crid=NPAIHMT6E263&keywords=unhindered+a+mindful+path+through+the+five+hindrances&qid=1649084275&sprefix=unhindered+a+mindful+path+through+the+five+hindrances%2Caps%2C55&sr=8-1\