I need to create a GUI to interface with Keyence PLC from a PC. However, I'm new to this area and so am not sure how to start. Any help is appreciated on how about doing this.
Find an online catalog for some graphical user interfaces. Then read the specifications to find what PLCs they will work with. I can give you a list of popular ones in the US, but they might not be available in Singapore.
Click this link to go to Keyence's download section. You may need to register to download.
Choose the instruction manual of the PLC you are using. The instruction manual contains all you need for serial communications with the PLC. It is a 'Command' / 'Response' type communication.
This is the most basic (low level) method of communication with these PLC's. If this is too involved then do as Lancie1 suggests.