Well they are not a big deal to install yourself!But to your questions......
Wireless is not faster. The speed depends on your internet connection...namely the wires into the box from the phone lines and what is going on at the Interst Service Provider end (ISP)! The wireless bit is how you get it from that supplied box to your computer.
Most laptops come with wireless inside.... desktop PCs not necessarily.
Wireless is great for laptops. You can wander around the house and even out into the garden and still connect to the internet, no wires see.. Other members of the household can too, at the same time. A wireless printer is nice, a printer sat anyplace that you can send to without wires.
First thing, find out about wireless for your PC... does it have it. do you need to buy it. But don't worry the wireless modem/router will have places to connect the old style 'network cable'. If you are going to keep the PC near the modem/router, a cable will work...also if no other computers or remote printers will be used in your home, no need for wireless.
One thing to beware.... if a technician sorts it for you, and makes the wireless network 'secure', as he should... get the password off him! They are twats for keeping it to themselves then you have to pay for him to come back one day!