How to become a strong communicator? How to the little English you know in an effective way?

I think, I reckon, I believe…
今天我們學習的重點就是要看看如何用最簡單的單詞來表達出自己的看法。

"I think…" is a very neutral way of giving your opinion. "I believe…" is slightly more formal. A very informal way is to say "I reckon…".
I reckon it"s gonna rain later.
"I believe it's going to rain" would sound a little bit formal.
今天的節目中重點介紹了"reckon"這個詞,它的意思是"想,認為",比較的非正式.

If you a very strong conviction about sth, you might say sth like "I strongly believe that…", or "I am absolutely certain that…".
If your don't have a very strong conviction about sth, you might say"I'm not so sure,but…"

Ways of responding:
Exactly.(if you absolutely agree with the speaker)

Well, I agree up to a point, but…(if you don't really agree with the speaker)

If you disagree, you can say "I disagree", but it's not very natural. It is better to say "oh, come on…".