why does price move back & forth within a range?

I guess it is because of indecision on the part of buyers/sellers. Perhaps they could be waiting for a certain news to be released before they place big trades. On the eve of Nonfarm payrolls, CPI, interest rate news etc. we usually see this kind of ranging behavior. However, after the news is out, the market resumes its normal motion.

hey, what would you do if you were trading this chart, would you buy or sell?

The dominant trend is a bullish engulfing signalling a buy. Price has not been able to close below the bullish engulfing pattern hence the support linne i drew.