چه موقع از گذشته ساده استفاده کنیم؟ گرامر مبتدیان

In this video, Alisha answers 5 questions.
- What's the difference between 'By myself' and 'on my own'? What's more casual?
- What is the difference between suitable and convenient?
- When we can use "I was there", "I have been there" and what is the difference?
- I have come across a word called "Baller". Could you plz explain what actually it means?
- What is correct and why: I have saw or I have seen?