简单而言：
to后面一般加的是动词原型,
eg.I want to eat an apple.
Would you like to go to library with me this saturday?
for后面一般加的是名词或动词的名词形式.
eg. Water is essential for people.
但愿对你可以有用.

如果还不懂 请追问名词形式什么意思比如read,它的名词形式就是reading,也可以理解为进行时