They are only allowed to search areas that might contain the evidence they are looking for, and that are specified in the warrant. For example, if the police suspect you have hidden in your house a rifle that was used in a crime, they will attempt to get a warrant to search those areas where a rifle can be found. That usually means that they can look under beds, in closets or behind doors. It will not authorize them to look into your bedroom drawers or kitchen cabinets for the rifle, unless there is the possibility it would fit into one of those areas. The police cannot simply break down the door to gain entrance into your home.
Every person has an important constitutionally protected right to privacy in their homes.
If the police have a warrant, they are supposed to knock and announce themselves first. If the police come to your home just to ask questions, you can can simply close the door and refuse to talk, or refer them to your lawyer. This is your right in every state. If they want to enter, they have to get a warrant. If they already have a warrant, and you shut the door on them, they can legally break in.