used to do 和 to do 是两个不同意思的词组,并有不同用法.
仅 to do 两个单词不可接动词,要接名词,
但 used to do 可接名词和很多动词,比如（下面举一些 a 到 h 的例子）
act
ask
answer
bring
buy
call
come
cry
dry
enter
fall
forget
fry
give
gobble
groan
hang
hit
如果你是说
use sth to do sth ...
这个词组里的第二个 sth 必须是名词或名词短语,比如
You can use a computer to do many things
You can use others to do things for you
Humans use elephants to do jobs which are difficult,like lifting heavy objects.