Keto / Low Carb

Hello I am new to the keto / low carb diet. I am looking to get into it. I just have a few questions. I am a bigger guy and don't know how many carbs I should consume in a day.

Are you able to eat fruits? I like to have smoothies I make at home. And really like to blend a banana and add it to my iced coffee. Would I still be able to have that?

I am trying to use the MyFitnessPal app. Is this a good app to use or should I use another one? And what should I set my targets as?