How do you communicate with the people you don't share the same mother tongue?

Language is the key of communication since the exsitence of humanity. I think it was simplier in the past. The language people used was less complex, it was all about sounds but not the structure. Then, It has been evolved in a more complex way. Now, every language has several units and it is not an easy task to speak every language very fluently. So, how do people from different parts of the world communicate each other? The answer is quite simple. They speak a common language. Sometimes they can create this language together. While processing it, they use the simplified form of that language because generally they need that language for a specific reason such as trade. In linguistic, it is called 'Pidgin'. Pidgin is a grammatically simplified form of a language. Moreover, they can be the mother tongue of a generation. then we call them creol. If a child exposed to pidgin as a target language and speaks it as his/her first language, it can evolve a creol. Creols are more complex than pidgins. As you can read, people can make significant changes on languages in accordance with their necessity. Because communication is the most important thing for humanity.