How to buy stock after post market

1st i want to know shall we buy stock after post market closed or before pre market open.
2nd
What is the full form of BO CO & AMO
&
IOC?

AMO does the same thing. It is After Market Order.
BO/CO are leveraged/margin products.
Please refer to https://zerodha.com/z-connect/tradezerodha/zerodha-trader-software-version/bracket-orders-trailing-stoploss-sl for more information.

IOC (Immediate or cancel) for orders to be cancelled if not filled completely immediately.
More info: https://kite.trade/docs/kite/#advanced-order-types