Wow, that's a hard question ^_^ To say it short: "a" is use when you want to separate 2 things and "i" is used to connect something. Example: 1. (Poszłam do biblioteki, a moja koleżanka poszła na zakupy.) (I went to the library, and my friend went shopping.) "a" was used to express that we went to the different places. Also, it mean something like "about" so you can translate this sentense in english this way to express it better: (I went to the library. But what about my friend, she went shopping") 2. (Kupiłam zeszyt i długopis) (I bought a notebook and a pen) (Ja i moja koleżanka poszłyśmy do kina) (Me and my friend went to the cinema) "i" has to be use. So "i" means exactly "and" ___________________________________________________________________________________ It was hard to explain but I hope thet I helped a little. Just "i" means exactly "and" but "a" is more complicated as I wrote before, it shows the difference between to things but connect it into one sentense. If you need more examples then let me know ^_^ Take care~