I am a new developer, A List screen was designed by another company, I would like to see how this screen gets populated using which SQL tables. Is there a way to see this using AL ? Editing an exisitng screen? (this screen is not in the standard Business Central)
Welcome to DUG! And welcome to the BC world!
Everything you display in BC is displayed via Pages. Here you have list pages, card pages, worksheet pages etc.
If you want to add a new page, then you must create an extension written with the AL Language (using VSCode) with a new page object.
If you want to modify/edit an existing page, then you must also create an extension. But here you create a page extension object, which allows you to add and remove fields etc. from the page. If the field is not already in the table, then you can create a table extension (object) which will add new fields to the Business Central table. Technically this table extension is not modifying the sql table, but a new table which is joined by BC whenever used.
There is off course much more to it, but this is the very basic. Hope it answered your question - even if it may just have opened up a lot more!
Check out the download/resource section of this group, here you find many videos on how to get started with BC.