To set up PHP with Composer, you need to install the `composer` package manager on your system. Once installed, you can create a new project and initialize it with Composer by running the command `composer init`. This will create a composer.json file that contains metadata for your project. Next, you can add dependencies to your project using the `composer require` command. To push packages to Cloudsmith, you need to create an account on their website and set up a repository. You can then use the `cloudsmith push` command to upload your package to the repository. Additionally, you can use Composer's built-in functionality to automatically generate a Cloudsmith API key for your project. The official guide from Cloudsmith provides detailed instructions on how to set up PHP with Composer and push packages to their repository.