How to deploy custom code on D365 ?

Overview of the process 

In order to deploy your code and customizations to a runtime environment (Demo, Sandbox or Production), you must create deployable packages of your solution or implementation. Deployable packages can be created using the Visual Studio dev tools, or by the build automation process that are available on build environments. These deployable packages are referred to as Application Deployable Packages or AOT Deployable Packages. The image below is an overview of the process. Once a deployable package is created, it must be uploaded to the LCS project's asset library. An administrator can then go to the LCS environment page and apply the package to a runtime environment using the Maintain > Apply updates tool.

Note : Application Deployable Packages do not contain source code.

Create a deployable package

After you have completed the development stage, follow these steps to create a deployable package from Visual Studio.

1. In Microsoft Visual Studio, select Dynamics 365 > Deploy > Create Deployment Package. 
2. Select the packages that contain your models, and then select a location in which to create the deployable package. 
3. After a deployable package is created, sign in to Microsoft Dynamics Lifecycle Services (LCS), and then, in your LCS project, click the Asset Library tile.
4. Upload the deployable package that you created earlier.

Apply a deployable package

Apply updates to a cloud environment :

Note :Applying packages causes system downtime. All relevant services will be stopped, and you won't be able to use your environments while the package is being applied. You should plan accordingly.

Supported environments

The following topologies support package deployment that uses automated flows in LCS:

• LCS Implementation Project – All environment types are supported. Automated package application is a self-service operation in all environments except production environments. For production environments, customers must use LCS to submit a request to apply packages.
• LCS Partner and Trial Projects – All environment types are supported, except multi-box dev/test topologies.

For other topologies (below), you must use Remote Desktop Protocol (RDP) to connect to the environment and install from the command line. 

Source:MSDN