Simple answer – just DON’T!
Attempting to connecting the generator to your house without a transfer switch can cause serious damage to the electricity grid. It is also potentially hazardous for your health due to the risk of electrocution. In the worst case, it can be fatal.
Unless you are a DIY expert when purchasing a generator transfer switch make sure to hire a professional electrician to set it up. Trying to install it by yourself without prior experience can be dangerous and is NOT recommended.