第一，“that”在英文中可以用作形容词
That boy is clever.
第二 ，用作连词，引导名词性从句,状语从句和强调句。
I didn't expect (that) he could win the championship. （宾语从句）
That the earth goes around the sun is known to everyone. （主语从句）
（It is known to everyone that the earth goes around the sun.）
The trouble is that we are short of money.（表语从句）
The news that he resigned from office surprised us.(同位语从句)
It is me that have finished the task。（强调句）
I am afraid that I will fail in the driving test.（状语从句）
第三， 用作代词，既可作指示代词
也可用作关系代词，引导限制性定语从句。先行词可人可物，用法相当于who或which。
但是在下列情况下多用that：先行词既有人又有物时；先行词有形容词最高级、序数词、先行词是anything，everything，none，nothing等不定代词时、very，only little all 等修饰时；先行词是不定代词时。
请注意，that 在定语从句中作宾语时可省略。
The dog(that)his mother gave him will make him happy.
第四，用作关系副词，引导定语从句可以省略。
I was so happy that I couldn’help laughing.
I will never forget the morning(that) / when we played football.
与that 有关的常见重要短语。 now that(既然)， in that (由于),
seeing that (由于) see (to it) that（注意、务必做到）
追问什么叫名词性从句,状语从句和强调句宾语从句主语从句表语从句同位语从句
追答that的意思是“那，那个，那个的，那样”作形容词That boy is clever.
作代词That is a book.作副词I am that/so angry.在从句中作连词。所谓从句，就是一个主谓结构相当于整个句子(这样的句子叫复合句)的一个成分，因此，从句不能单独使用。在主从复合句中，从句可以充当主句的主语、表语、宾语或同位语。由于在多数情况下，主语、表语、宾语或同位语这四种句子成分由名词性词类充当，所以，我们把这些作用相当于名词的从句统称为名词性从句，把充当主语、表语、宾语或同位语的从句分别称为主语从句、表语从句、宾语从句或同位语从句。一个句子在整个复合句中充当状语就是状语从句，也就是说充当什么成分就叫什么从句。