summer often hot ,we must go to the used.这句话是否正确?

不对.可以改为：
Summer is often hot,we must .
请问楼主：后面这一半你想表达的是什么意思?
but we must get used to it.
get used to 是固定短语,“习惯于”的意思.后面要接名词或代词.
两句话合并起来说就是：
Summer is often/usually hot,but we must get used to it.夏天常常是很热,但是我们必须习惯于它.