Many students struggle to understand when to use the past simple and when to use the present perfect.
We use :
Past simple - to talk about the past
Present perfect - to talk about the past if it is connected to now
Understanding the connection to now is a very tricky concept to master. It's something that teachers spend a lot of time explaining and students spend a lot of time practising.
How to practice
One way to develop your understanding of English grammar is to analyse the choices made in authentic texts. This is something we sometimes do at the start of our conversation classes. First we make sure we understand the vocabulary and the grammar choices in the article, then we talk about the topic.
This article from The Guardian contains some good examples of the present perfect being used rather than the past simple. Try to identify the reasons for the choices made. Change some of the present perfect sentences (have/has + past participle) to past simple versions then decide which sentence is better. Why has the author decided (subconsciously) to use the present perfect?
Find other articles and try to analyse the language choices in just one or two paragraphs. The more you notice how language is used in real life, the better!