A proposal from a company or person who wants to sell you something can use the word offer to make it sound a bit more inviting. You should read the offer carefully so that you are completely sure about what it means. If you are not sure, ask! You must be completely sure about what you have to give to make use of the offer. In principle this always involves money, even though this may not be stated clearly in the offer. For example, it is common to be offered the chance to join a book club or something similar and then you get several free books and a bag or some other present. The point is that you must always do something to get this, it is not free. Often the idea is that you must buy a certain number of books (or whatever the offer is for) before you can leave the club.