我跟他说:是向第三人称（他/她）说的话 而第二人称（听话的人/你）不知道说话的内容。 我给他说：是向第三人称（他/她）说的话，但第二人称（听话的人/你）知道说话的内容。 我和他说：是向第三人称（他/她）说的话，第二人称（听话的人/你）有两种可能，一，知道，二，不知道。 我替他说：多数都是第一人称（我）向第二人称（你）说的话，但内容几乎来自第一人称。第三人称的（他/她）可能根本不知其内容！ eg:我替他说：对不起！其实。这里的他根本不知道。但在代替问候方面的，第三人称（他/她）是知道内容的， 可能有点复杂。但本人英语不好，希望有的高手帮着翻译一下也行！！！！仅个人理解！！！

我跟他说 means 我和他说. Both of mean is that I tell you something. We uaually don't say 我给他说. 我替他说 means you help someone to say something.Its meaning is different from 我和他说.

我和他说=我跟他说 they mean i tell him.我给他说，it has the same meaning,but i think it dialect.it is used in some places. 我替他说。means you help someone to tell others.for example,you have a friend want to tell us a story,but he is too shy to speak a word,so you say :ok,i will tell you this story for him.this is 我替他说

“我跟他说”,“ 我和他说”意思差不多。 “我给他说”一般不用 “我替他说”does not mean “我跟他说”or“ 我和他说”

跟 and 和　＞＞＞They are almost the same, but the word "跟" usually has a active meaning. Let's take the sentence "我跟他說" as an example, the direct translation in English is I tell him or I talk to him. But 我和他說 is more like to the meaning of I talk with him. As to the usage of 給, in Chinese it usually (not exactlly )has a passive meaning , such as 給我看 >> Let me see. (the object is about to be seen by me) or 把門(給)關上>> Close the door. Here's a little different as you see the word 給 is optional in this context , yet it still has a passive meaning which is let the door be closed.