The mandala starts with a single point at it’s centre which symbolises the unity of all things. It grows out from the centre, from unity to duality, this is symbolised by the Yin Yang design. This splits into eight directions that represent the eightfold path of Buddhism. It’s circular shape transitions into a four sided square that represent the four noble truths of Buddhism.
Four Noble Truths

Dukkha; The noble truth of suffering
Samudaya; The arising or origin of dukkha 
Nirodha; The cessation of dukkha
Magga; The way leading to the cessation of dukkha 
The way leading to the cessation of suffering is the eightfold path