Well this is a broad question but my best advice would be to check the official Magento 2 samples.

You can find them here: https://github.com/magento/magento2-samples

This project is a collection of samples to demonstrate technologies introduced in Magento 2. You will find the most simple extension along with samples that incrementally add features to lead you through a exploration and education of the Magento 2 platform.

On top of that you can find many tutorial if you search "magento 2 create module" in Google

Well this is a broad question but my best advice would be to check the official Magento 2 samples.

You can find them here: https://github.com/magento/magento2-samples

This project is a collection of samples to demonstrate technologies introduced in Magento 2. You will find the most simple extension along with samples that incrementally add features to lead you through a exploration and education of the Magento 2 platform.

On top of that you can find many tutorials if you search "magento 2 create module" in Google