Why translators use their own words when they translate things . and are they exactly when the speaker is trying to say?

If you're talking about translation done on the spot like those done for presidents. I think that's because the main need is speed. When someone is speaking at a conference, or a seminar, etc... It's more important to deliver the meaning of the speech quickly in any correct phraseology than to deliver a translation with a specific phraseology2 minutes later. Everyone uses a unique way of speech, yet they're all correct and have the same meaning. And as to the second question. Yes and no. A speech could have parts that aren't of utmost importance which the translator could translate in a general meaning and others which are very important and should be translated on a word to word basis.