'Laters' is a very informal and colloquial form of 'see you later'. 'woop woop' is similar to 'wahoo' or 'hooray'. It's the sound of a yelled out cheer. Again, it's very informal. It is probably intended to mean something like 'congratulations. You need to be careful interpreting it though, as it is often used in a very sarcastic way, to mean the exact opposite. It is an unusual piece of writing, as 'we regret to inform you' is very formal, then it ends up with 'laters', which is the complete opposite. It also is a little nasty, or teasing - as from the 'you have a place here' - we can interpret that the person getting the message probably applied for a place at a school, or academy. By starting with 'we regret to inform you', they are trying to sound like they are going to say that they haven't got a place, but then go on to say that the regret was for something else.