The buy and sell volume is the number of shares that have been traded during a trading session. This does not indicate the amount of shares available for purchase - that will depend on the order book. A transaction is determined to be "bought from seller" when traded at the ask price, and "sold to buyer" when traded at the bid price. Thus, from the information you provided, it means that during that trading session, 1500 shares were bought at the ask price, and 300 shares were sold at the bid price, for a total volume of 1800 shares.
A better measure would be to look at the average volume, which measures the volume over a timespan of 30 days. Apart from volume, you should also look at the bid-ask spread, as higher bid-ask spread usually results in larger tracking error. I've attached a screenshot from IBKR as an example below.
SWRD is issued by SSGA, one of the largest ETF issuers in the world alongside Vanguard and Blackrock iShares (who issues IWDA). Its main advantage is its lower expense ratio of 0.12% compared to IWDA at 0.20%. Since it is relatively new, it suffers from lower volume and higher bid-ask spreads compared to IWDA. In the long-term, as investor demand increases, this should become less of a problem, and should not affect the value of your investments anyway. However, in the unlikely scenario that SWRD remains unpopular in the long run and closes down, the switching costs could outweigh the savings in expense ratio.
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