I think it depends on the kind 200 words you know.
There are words that occur most frequently in our day-to-day conversation, they are the building blocks of common dialogues in Mandarin.

Some essential verbs such as:
Eat (吃), run (跑), write (寫), look (看), say (說)
All pronouns are important. You should know all of them. Such as:
You (你), You all (你們), I/me (我), we/us (我們), he/him (他), They (他們/她們/它們
).
This (這), that (那), this one (這個), that one (那個),
You need some words to be able to tell places. Such as:
This place (那裏), That place (那裏).
It is also essential to be able to count and know how to say Monday, Tuesday, all the way to Sunday in Mandarin so that you will be able to describe time and days of the week.
Adjectives are important. Words like big(大), small (小), good (好), beautiful(美), fast (快), slow (慢), cold (冷), and hot(熱).
You should know how to negate a concept using not (不). For example, not big(不大), not small (不小), not good (不好), not beautiful (不美), etc.
In the end, with some nouns that you’ve already learned, you should be able to create sentences on your own. A good deal of practice is required to learn to be able to apply these Chinese characters without too much conscious thinking.
Depending on how much work you put in, I would say it takes anywhere from a few weeks to a few months to be able to carry out simple conversation with people in Mandarin. Find some partners/tutors/teachers here to help you achieve this goal. Good luck and hope you enjoy learning it!

I have a book named "Chinese Idioms and Their English Equivalents", edited by 書林 (Taiwan).

You may look up in a dictionary, for example, 成語詞典.