Luckily, there is no hub required to use the Apple Home app to control your HomeKit devices when you are at home. If you want to control them remotely when you are out of the house and away from home, you will require a third- or fourth-generation Apple TV with tvOS 9 or later, a HomePod, or an iPad running iOS 10 or later. Any of the mentioned devices would act as the home hub and would have to remain at your home to remotely control them while you are away and to create any automated actions or timers for your devices.

Apple Support's Home Hub Setup Page: https://support.apple.com/en-us/HT207057

With Automation, you can turn off all the lights when you leave, turn them on when motion is detected, or run a scene when you unlock your front door. With the Home app, you can automate your accessories and scenes to do what you want, when you want. Options to create automation can be based on an action, on a person's location, and based on a specific time of the day and/or day(s) of the week.

Apple Support's Automation Setup Page: https://support.apple.com/en-us/HT208940