I tried Goggling it but can't find the answer. I have seen many tutorials but all says that the Arduino on breadboard is not capable of Serial Communication.
As is so often the case, you are clearly misinterpreting the descriptions. It is perfectly capable. A "breadboard" or custom PCB will be capable of serial communication if you include the serial communication circuitry. Such circuitry is of course included in the UNO and similar, but not in the (Pro) Mini. You build what you need.
The question then, is what "serial" interface do you need? If you need TTL communication, then it is already there on (port) pins 0 and 1. If you need RS-232 levels then you need to include a MAX232. If you want USB functionality, then you need to use an FT232 or CP2102 (or a third option that I do not have on the tip of my tongue).
The thing is though, unless you want to make a number of these, it really is a waste of time and money to (design and) make PCBs; the Chinese modules are essentially as cheap as the chips themselves and perfectly robust. If you need to add extra components, you can use a perfboard (with solder pads, or a "breadboard" version) with the module mounted (soldered by the pins) to it.
If you need the USB interface, you can add one of the cheap modules, or consider buying a "nano" module with it already included - essentially a miniaturised UNO. Or the "pro micro" which is a miniaturised Leonardo.