It is not necessary to understand every single word.
Try to ignore those words that you think are less important anyway.
If there are words or issues that you don't understand, use your general knowledge as well as the context to find out the meaning.
If you still don't understand something, use a dictionary to look up the words or ask someone else for help.
Focus on key words and facts.
Take notes to support your memory.
Intonation and stress of the speakers can help you to understand what you hear.
Try to think ahead. What might happen next? What might the speakers say, which words might they use?