The four noble truth is basic principle of Buddhism or is also known as foundation of Buddhism. The person who wants to study Buddhism has to understand these four noble truth at the beginning which are as follows:
1.Life means suffering (dukkha)
It doesn't mean there is no happiness at all but it means happiness is not permanent and there is always suffering. Like we suffer from illness, we don't like to get old, we don't want to die, we don't always get what we want, we have to stay apart from our loved ones,etc. There are uncountable sufferings that one has to face in his lifetime.
2.The reason behind suffering is craving (samudaya)
There is always some cause behind suffering. Like we want something and if we don't get it we'll get sad, if we get it we will be happy but we will be bored after some time and we will search for something else. Likewise our desire never ends which is leading us to the suffering.
3.The cessation of suffering (nirodha)
We can end suffering by ending the craving. Like if we don't desire then there is no need to fulfill it then there will not be any sadness. Its like we should not be attached to anything because attachment brings all the sorrows.
4.The middle way (magga)
It means the noble eightfold path which should be practised to end the circle of suffering life.