In spoken English, certain words are stressed while others are reduced, creating rhythm and intonation. The stressed words typically carry the main meaning and are usually nouns, verbs, adjectives, or adverbs.
For instance, in the sentence ‘Can you pay by cash?’ ‘pay’ and ‘cash’ are stressed.
By focusing on these stressed words, you can grasp the main idea more quickly.
Here is an important study tip. When you are doing listening practice, you should practice both intensive listening, where you listen to short clips of say, 30 to 60 seconds, and focus on understanding as much as possible, and extensive listening, where you listen to longer clips (podcasts, films TV shows) and focus on understanding the main ideas, not everything.
When you do intensive listening practice, focus on sentence stress and picking out the keywords that are stressed. That is usually enough to get the meaning. Forget about the other unstressed words. This is actually what native English speakers do, so why not try it too?