to be simple, universal life = life insurance+ investment. Hopefully 20 years later, your investment account will cover your life insurance premium. But, there is not guarantee your investment will grow large enough. If the current economy trend goes on for 20 years, you have to pay more 20 years later. (But that's impossible.) Because they invest in stock market and mutual fund.
whole life means u pay premium for your entire life. But there are a couple of variations, such as Term 20 and Term 10, that requires your premium within only 20 and 10 years separately. And Whole Life invest in GIC account. So, there is guarantee.
By the way, there are other differences. such as tax defer, premium holiday, etc. Why don't u find an expert who sells life insurance?