Hello Sara,

The lesson that you are referring to is about ways of talking about the weather and references the use of "hay [impersonal there is / there are]" and "estar [it is]." They have to be learned off. We don't have the "it is" difference in English when talking about the weather. 

There is a linked lesson to the use of "hace" when talking about the weather. It always translates as "it is." Allow for the fact that there is a bit of overlap; "esta soleado and hace sol" both translate as "it is sunny." Again you just need to learn them off. 

I haven't come across any other insights about the topic on this forum, but this is idiomatic usage and if you think in terms of learning set phrases which are ways of talking about the weather it will come more naturally.

Good luck. John