Which part are you struggling with? This basic summary from reddit (https://www.reddit.com/r/BitShares/comments/6h4j2y/what_is_bts/divugh5/) explained it quite nicely I thought:

It's a coin (symbol BTS), like Bitcoin (BTC), but also a platform (which can lead to some confusion). You can own and trade Bitshares (BTS) as you would any other coin (ETH, BTC, DASH etc) - for example on Poloniex - pair BTS/BTC), but the real magic is the platform which is like an entirely decentralized financial ecosystem.

The Bitshares platform covers features such as;

• The DEX (Distributed Exchange): An exchange like Poloniex or Bitfinex for example, but one that isn't centralized and anyone can use. Install the client at bitshares.org\download and take a look.

• UIA (User Issued Assets): Equivalent to stocks quoted on the New York Stock Exchange, but created by users of the Bitshares platform by locking away some of the BTS they own (Similar to how a company creates shares). User Issues Assets can then be traded on the Decentralized exchange in the same way as people trade stocks on the NYSE. For example; you could set-up a company, get people to fund you some BTS (or use your own), create your own UIA (just like all companies that have an Initial Public Offering - IPO - do) and return those people your UIA in exchange. People can trade your UIA based on how well they perceive your company to be doing, just like on the NYSE. You just floated your company! (with crypto)

• SmartCoins (Pegged Assets): Are similar to UIA's (In that they require BTS is locked up for them to exist), but rather than having a free floating value their value is set by the Bitshares platform (specifically by witnesses via Price feeds). A witness is equivalent to a miner in Bitcoin and a Price feed is a value that each witness publishes to the Bitshares platform saying what how much a SmartCoin should be worth in BTS. This clever mechanism allows a SmartCoin to have a price pegged to a real-world instrument (for example the US DOLLAR, EURO or CHINESE YUAN), but valued in Bitshares (BTS). The SmartCoins are backed by BTS (so if BTS is worth nothing, then they'll be valueless), but - if you assume BTS is worth something - then by exchanging your BTS for a SmartCoin (E.g. BitUSD or BitCNY), you can effectively protect yourself from the huge volatility that surrounds BTS. It's no different to selling any BTC you own for USD (or EUR or CNY) on an exchange like Bitstamp or Bitfinex, except that Smartcoins are entirely decentralized (through the magic of the DEX), so not susceptible to the exchange disappearing with your money, forcing a loss on you because they were hacked or suddenly deciding to seize your assets because you don't meet their Anti Money Laundering / Identity requirements. All the benefits of a USD/EUR/CHY, but without the annoying drawbacks of centralization.

The Bitshares coin (BTS) is the oil that makes the Bitshares platform work. It acts both like the 'gold standard' that historically was used for backing fiat currencies allowing the creation of User Issued Assets's and SmartCoins, but it also acts like a share allowing those who own BTS to vote on what new developments should be worked on for the Bitshares platform or what settings should be changed (E.g. confirmation times, block sizes) etc. BTS can also be used and traded as a coin in the same was as people trade BTC/ETH/DASH etc.

That's just a simplified run-down of the best bits of Bitshares. It also has massive throughput potential (over 100,000 tps) and a number of other features, but probably most important of all; it exists here and now with all the features listed above, usable by anyone who wants to get involved.

You can download the wallet from https://bitshares.org/download or register at a web-wallet (use Account model if you want to log in from any device or computer) like http://openledger.io/ or https://bitshares.org/wallet/