that's all的意思是这就是全部。例句：That is all I have to say.这就是我想说的全部内容。
例句
1、'I had no desire to be a mother — I had a child, that's all.'
“我不渴望当妈妈，我有一个孩子了，如此而已。”
2、I can boot up from a floppy disk, but that's all
我可以用一张软盘来启动，但其他的就无能为力了。
3、She's going through a difficult time. That's all there is to it.
她正经历一个困难时期。就这么简单。
4、You just don't want to go; that's all.
你就是不想去罢了。
5、That's all for today.
今天的工作就到此为止。