A Raspberry Pi is just a small motherboard with a processor, RAM, GPU in-built. Its a full fletched tiny computer in itself. However, you would still need to connect it to an external display since it does not have a display of its own.
The Raspberry Pi comes with an HDMI port on the circuit board which you can use to connect to an external monitor. If you have a monitor that supports DVI input, you would need an HDMI to DVI adapter. Similarly, if your monitor supports a VGA input, you would need an HDMI to VGA adapter.
What kind of a touchscreen display do you have? Does it have any input port that can be connected to an HDMI cable with or without the above adapters? If yes, then you can definitely connect the said touchscreen display to the Raspberry Pi.