Heya @Luanajo =)
No worries! Basically, if you send anything abroad you have to fill out a sticker that goes on the outside of the parcel saying what's in it, what it's worth (cost wise) and promising it's nothing dangerous =D If you send something to the UK with a stated value close to or more than about $72 (limit is 36GBP iir so the $ value does change - I'd be wary of anything over $50) our version of AQIS (the quarantine bunch) get hold of it, and won't send it on until tax has been paid on it. Everything over 36GBP has to have VAT (Value added tax) paid on it at 20% of the value of the parcel and then if it's worth enough then import duty has to be paid too (another tax). You may well be getting close to that amount with what you're planning on sending. Add it up and see... you may need to do some creative mathematics Don't lie about what's *in* it though as if they scan the parcel they will end up opening it etc.
From memory, although it isn't mentioned on the site, when it happened to me I had to pay some fee or other as well as the VAT - because these people love to charge for anything lol.
The other thing too, when sending stuff abroad, is to check what can and can't be sent. Australia is SHOCKING for what you can't receive. I don't think you'd have any trouble with what you're planning on sending though as the UK isn't particularly paranoid like that, but if they wanted to send you anything they'd need to check the AQIS website =D
Hope that made sense!! Ask if not =D