1) These three terms are very similar in nature and are often used interchangeably.The last two are almost exactly the same. Here are some sentences showing the difference: The mother showed 'concern for' her child. There was much 'concern about' the state of affairs in Ukraine. The term 'concern over' can be used in exactly the same way as 'concern about'. Both are correct 2) 'To go on' is a colloquial phrase in English which simply means 'get an idea of' or 'to make use of'. So for your sentence, all it means is that if one cannot provide a repairs cost, they must give an approximate amount for the others to get an idea of how much money is being spoken about. 3) 'Advertisings' isn't a word used in English. The word 'advertising' (without the 's') is a gerund and means 'to advertise' referring to the action itself. On the other hand, an 'advertisement' (or an 'ad' for short) means anything made with the intention of drawing attention to something else. For example commercials on TV/radio and billboards are examples of advertisements. 4) This is easy to remember. A noun is any "thing", for example anything you can touch, taste, see or hear. A noun can be described as any person, place, thing, or idea. A gerund is any word that ends with '-ing' (for example 'eating' or 'falling') Of course, these definitions are very simplified. English is a language full of exceptions and strange rules. I hope this helps :)

Those answers are really helpful for me, thanks a lot!