Before starting these steps for connecting your Brother printer to Wi-Fi, you should know these two things of your network:
First is network name (SSID),
and the second one is the security key of the network.
You can get this information on the backside of your Wi-Fi router. Look at the documentation given by the Wi-Fi router and access point.

Note: Make sure you have downloaded Brother Control Center.

Hint: Starting network name might be model or manufacturer name. You can also call the Brother Printer Support at +1-850-250-3133.

Note: attempted to connect the Wi-Fi earlier, then firstly, you must reset the wireless connection.

• First, connect your printer with the AC power cord, then connect the power cord to electricity.
• Now open the Control Panel on your Brother Printer to set up wireless.
• Now press the Menu button.
• Then choose Network settings or wireless/WLAN setup. ( to choose please use up or down arrow key)
• Now choose the setup wizard, Press-up & down button, then press OK after selecting the Setup Wizard. 
• Enable the WLAN Network when Local Area Network Enables. After this, your wireless setup wizard starts.
• Now let your Printer search for the Wi-Fi network & display the explored available networks.
• Now, at last, you have to choose your SSID, then press OK and type your SSID key.

Here`s your done.