Hi , if you are a beginner you will only catch the key words. Whilst you are organising your thoughts to work out your reply, smile & nod at the person you are speaking to. Another technique is to say, 'Can you speak more slowly please? I'm just starting to learn English'. That way you indicate to the person that they shouldn't use any slang that you might be unfamiliar with. Good luck!

You should just practise - speak with somebody and maybe read english books. It will help to make bigger your vocabulary. Good luck ;)

Hello , You won't be able to reach a degree of fluency *speaking fast* at once, it will happen gradually and you would sense an improvement ,if you keep practicing by reading ,writing and listening, which will increase your vocabulary and improve your fluency. The more you speak ,read loud and listen to speech *native is better*, the more efficient and fluent you will become. You might give up if you don't feel any improvement immediately after some practice, but you shouldn't. Just keep learning and you will sense the improvement in your speech by time .Lots of fun :)