sentence is "stocks offered a picture of contrast on thursday as the benchmark sensex snapped its four-day falling spell after the rajya sabha passed the historic GST bill on wednesday amid signs of strength in global markets"
"Stocks" is a way of personifying the stock market.
"Offered a picture of contrast" is an overly-wordy way of saying the stock market changed direction.
"the benchmark sensex" refers to the SENSEX, a numeric index of stock marked performance. (See https://en.wikipedia.org/wiki/BSE_SENSEX.)
"snapped its four-day falling spell": Reversed a falling trend. That is, a trend towards lower stock prices was reversed: Stock prices started to rise.
"rajya sabha" is a lawmaking body in India. See https://en.wikipedia.org/wiki/Rajya_Sabha.
"GST" is an initialism for Goods & Services Taxes. See https://en.wikipedia.org/wiki/Goods_and_Services_Tax_Bill.
"GST Bill" refers to a new bill that would decrease financial pressure on businesses doing commerce in Inida. See http://indianexpress.com/article/business/gst-bill-goods-and-service-tax-bill-arun-jaitley-here-is-how-india-inc-is-reacting-rajya-sabha-2951877/.
"amid signs of strength in global markets" would indicate various financial indicators that indicate a robust (i.e., growing) economy.
In summary: The indications of a stable or growing economy led India to pass a tax bill that indicated confidence in the economy, and that helped reverse a trend in falling stock prices.