This is not really a good explanation... I am aware of that but I will try. You use "i" for example when you describe where something is. "Where is the dress?" It is in the closet - "den är i garderoben". The word "på" also describes where something is for example "where is the plate" it is on the table - "den är på bordet". The word "till" doesn't describe where anything is. You use it more when you are telling where to go, "where are you going?" I am going to the city - jag åker till staden. You can also use "till" when you are telling that you are giving something away like "jag ger blomman till dig". I give the flower to you. "i" = in "på" = on "till" = to. This is the first time a try to explain my own language, I realise how difficult it is. Hope you get something out from my messy explanation. :)