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Help me understand shorting of stocks/ultrashort ETFs!!? - ultrashort etf

I am APecon and recently completed a simulation of events.

I understand the principle behind the short selling of shares (shares call high price of the shares, your stock in the open, cover if the price falls, the short). However, when it comes to ETF Ultra I am a little confused.

I read and found ultrashort ETFs, which are the inverse trend x2 NASDAQ, DOW, NYSE, etc. It is very confusing. As can be increased if the rest of the stock market to bottom?

So one of my friends was too little about the book told me that I should know about investing in an ETF SKF as Ultra, but it is short, when the price of 100-130 (at the lowest point) ..

But if I have an ultra-short ETF's like SKF, is not too close to me if the price is high (180 +), not when its low (100-130)?

I can not buy (good), if the price is 100-130 and sell when you reach 180 + on long-term investments

Short-acting immediately when their height and cover my short when it comes to 100New -130.

In this way you will receive benefits, regardless of the market?

I guess I'm confused with some terms or is it something about the ultra-short ETF I do not understand.

my understanding of the concepts:
Concept: The Sale of shares from the stock have borrowed
on a short, pay the amount you borrow money again (preferably after a decline in stock prices, after a short circuit)