For simple ports cut holes in the cylinder wall, 1 hole for the exhaust and 1 for the inlet transfer port. That sounds simple but the holes need to be at the correct height in the cylinder to ensure correctly timed opening/closing periods. For a simple engine the ports will be positioned opposite each other.
If the incoming air/fuel mixture is entering via the crankcase, from front or rear induction, then inlet transfer channel/s will need to be provided in the crankcase to the top of the transfer port/s in the cylinder.
The top of the transfer port will be lower than the top of the exhaust port but there will normally be some overlap of port to case openings (inlet,transfer,exhaust) this is useful if using a tuned exhaust system.
xpylonracer