英文句子什麼時候要加 "to"?

⒈在英文中to可以為介系詞或是不定詞

a.不定詞（ to +原形動詞)
而不定詞有很多最常見的
Ex：
hope to
Need to
Want to
Like to
Be able to
Would you like to…



b.介係詞後接動名詞/受詞/名詞（to+ Ving/O/N)
多為片語




2.若主詞為單數時動詞須加s
單數主詞
He/She/It或人名

Do 變 Does
Have變has
Ex：
I have a ticket.
She has a ticket.

I do it again and again.
She does it again and again.

基本概念:
一.
2個動詞之間=要用to隔開-->兩個原形動詞不能放在一起
二.
有的片語=會用到to + N(名詞)
意思是說:
to 不一定 + 原形動詞
三.
當作介係詞= to + N

請問:
have→has = 啥咪意思?看不懂!!
have = I / We / You / They + have
has = He / She / It + has

請參考:

http://english.cnfla.com/flash/1057.htm

1.像Want to、Like to......
2.第三人稱單數時