How does a person become addicted to a drug?

personally for me it a person gets affected to a drug when they use it all the time if they use it frequently just like people become addicted to tabaco and that's why it hard for them to stop the same goes with drugs and people also get addicted because some use it as an escape to their life if there going though something it easier for them to get addicted it a way they can work and they feel good so they start to do it every day but it may feel good to them but it's not especially people around them