With the increasing number of European High Performance Computing (HPC) systems and the targeted road towards Exascale computing, HPC applications always faced a diversity of different system types and environment approaches. Typically, one major task of each HPC application is the porting and code-optimization activity to take advantage of all system capabilities and to run the application with the highest efficiency. Normally the porting of an optimization work can not be achieved just by the application developer. HPC experts are typically involved during the certain stages of application development to help users in resolving all the possible issues arisen due to application porting as well to (guide users in achieving the maximum possible performance from the target high-end IT platform. Due to this support demand, various HPC support activities were established during the last years to offer general HPC knowledge as well as scientific area specific optimization strategies towards the research and industrial community. This guide provides an overview about the larger running application porting and code-optimization activities for European HPC systems. It does not cover specific technical details of certain application but guides application developers and users to the right project or activity, which can help in context of certain HPC codes or scientific areas. This guide will start with an introduction of EuroHPC, which deals a framework for several upcoming application support programs. The third chapter covers the porting and optimization activities within the PRACE-6IP project such as Preparatory access, SHAPE or DECI. This section is followed by an overview about the current generation of Centres of Excellence on HPC. Finally, examples of national HPC support activities are given.