need help adding my Canon MB2120 printer to my MacBook Pro 9th generation

That printer is capable of being connected to your Wi-Fi network as a station, and accessible from every device within range of your Router.

Many printer makers seem to think its is a really "cute trick" to allow your phone to print directly to the Printer. To that end, their default is to turn the Printer into its own Base Station. In a crowded area, this mucks up the Wi-Fi for everyone, and does not work well, and does not allow printing from your Home Network.

So the biggest thing you have to overcome is the maker's zeal for this "cute trick" and set your printer up "the right way" so that it can be used by all devices on your Network.

to do this over Wi-Fi, the Printer needs to know three things:

1) what network-name is it supposed to join

2) what is the password to get on that network

3) how is it supposed to get an IP address (DHCP or manual at a specified address)

without all three of these, it can't join your home network, so it can't be 'discovered'.

There are basically two ways to get these into the Printer:

a) fat-finger it in through the printer's "front panel"

b) connect using a USB cable first, tell it the stuff, then disconnect the cable

There is one more way, but it is unbearably inconvenient. Leave the USB cable connected and the computer powered on at all times, and print over the network to a queue on the connected computer.

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In addition, the path of least resistance is to use the AirPrint Drivers. Again this is part of the cute trick of printing directly from your phone. The problem with that is you get NO Access to printer special features such as alternate paper sizes, two-sided printing, manual feed, and features you paid extra for.

You must take great care to select the driver intended for Network use, not the (Often default) AirPrint driver.