Sounds like you need a basic Point of Sale course . . .
The steps you would take, at a very high level, are:
- input the part number, if not in stock create from price file
- add quantity required
- set to an order status (configurable but often V[OR], W[eekly], C[ollect], S[tock])
- save the WIP
in Purchase Control,
- attach the lines to an order header for the order type chosen
- transmit the order to the supplier
- receive the goods in when they arrive
in POS
- order status has changed to R
- Change status to P to pick
- issue the parts physically
- save the WIP
A lot of this is configurable by POS parameters.