usual是形容词,意思是通常的,常见的,平凡的,普通的.形容词修饰名词,说明事物或人的性质或特征
Foreigners learn Chinese in the usual ways.
(外国人通常都用这种方法学习汉语.)
而unusual是不寻常的,就是在usual的前面加上前缀un,表示否定.
It is unusual that winter comes so early this year.
(今年很不寻常,冬天来得特别早.)
usually是副词,意思是通常,经常.副词主要用来修饰动词,形容词,副词或其他结构.
He usually goes to school by bike.
(他通常骑自行车上学)