To join a COST action is an excellent way for you to build your international network, also for young researchers like PhD students and postdocs
The European Cooperation in Science and Technology (COST) is a funding organisation for the creation of research networks, called COST Actions. These networks offer an open space for collaboration among scientists across Europe (and beyond) and thereby give impetus to research advancements and innovation.
To learn more about COST and join a COST action, visit their website : https://www.cost.eu