When braking the front end shakes and makes a sound like I have a flat tire.

Hello, sounds like the front (and possibly rear) brake disc rotors are "out of round", warped. This will cause sometimes terrible vibration only when pressing the brake pedal. Brake rotors can be resurfaced to a minimum thickness, at which point they must be replaced if they cannot be resurfaced enough to take out the warpage. A technician will measure "runout" - the amount of warpage that exists and will determine the best action to take. Note that you should be changing your brake fluid every 2-3 years, as overheating brake fluid due to moisture intrusion is a common cause of brake overheating which can lead to brake rotor warpage. Seek local guidance at a shop near you if you would like: https://repairpal.com/auto-repair-near-me