There are two types of dependencies in magento 2.
Hard dependencies refers that a module can not be run with other dependencies on which it dependes.
Soft dependencies refers that a module can function without other dependencies on which it dependes.
There are three main steps for managing module dependencies.
1- Define the name and declare the module in module.xml file
2- Declare any other dependencies that the module has on other module in composer.json file.
3- Define the Sequences / Load Order in module.xml It is not always important.