We use the term market to imply the exchange of goods and services without the use of state money (legal tender). Private persons, self-employed people, businesswomen and companies can all become members. Note that this is very different to a shop, since each trade requires prior individual agreement by both parties.
All members of the market community get an account whose currency is the complementary trading currency Grok. The consulting service which Ms. Smith has provided to ABC PLC is paid for by ABC PLC through a transfer of the agreed amount of Groks onto the account of Ms. Smith.
The Groks do not exist as physical cash – there are no notes or coins.