When you fill out some form with an address. For example, when you set up bill payments in your bank account - among other fields you will see Address Line 1.
What should it be?
Unlike Address line 2 which is optional, Address Line 1 is required and you cannot finish your application without it.
In address line 1 you have to put a street address which should include the street name and house number
Let's take an example of such an address from Google Maps.
If your address has only a street name and house number - it should fit in Address Line 1.
In the second example from Google Maps the address has not only street and house, but also has a suite which should go straight to the address line 2. So in address line 2 you should put anything that is not part of the street address and should help with addressing the right person or department.
In address line 3 you can put city, state and zip code.
In line 4 you can put the country name and postal code.

Read more on slava-money.com
https://slava-money.com/what-is-address-line-1-and-address-line-2/