gotta用法是什么时候是's gotta,什么时候直接用gotta.那个's是 has 我很费解,请讲仔细点.

1. be gonna = be going to,口语常见用法,注意前面要有be,后面跟动词原形.
Are you gonna be there if I was down? 我失意的时候你会在吗?('N Sync: Are You Gonna Be There)
I'm gonna run away and never say goodbye. 我要逃掉,不辞而别.(Linkin Park: Runaway)
I am gonna be there at 3:00. 我三点时会到那.
(这句话也可以说成, "I am going to be there at 3:00." 或是 "I will be there at 3:00." 也是蛮常用的. 此外, 老美也喜欢说, "I will catch you there." 例如二个人约好要在体育馆见面, 你就可以说, "I'll catch you in the gym.")
2.gotta=got to (相当于have to 不得不,必须)
There's something I gotta tell ya我有点事要和你说.
I've gotta get outta here.我得离开这儿了.
I've gotta catch the bus. 我要去赶公共汽车了.

gotta就是have got to的意思,那么如果加‘s就是 has had got to的意思，就是时态改变了而已，明白了吧？