I try to dose my naked portafilter which i purchased a month back with 12gm of coffee and try to dose and tamp it properly. But most of the times i get a slightly burnt taste and also when i try to remove the puck from the filter, a part of it comes out and a part is stuck to the bottom of the filter. Not able to figure out where the problem lies.

Burnt taste - you might want to try better beans.

Puck - don't worry about how the puck comes out. It does not matter and does not tell you much about the quality of the coffee in the cup.

This is really hard to diagnose because there is really not much info to go by in your post. 12g sounds like a small dose, but no idea what your equipment is (grinder/machine), what coffee you are using and its roast date, what portafilter basket size and type, your total shot time, pressure, etc. If this is pretty new to you, you might check out the FAQ to see if it answers some questions. Otherwise, a simple cellphone to YouTube video often helps.