Just take a moment to enjoy Tim Bowen's explanation of the uses of this really handy word. It might just be worth your while!
If you want to make a request more polite, or perhaps a bit more tentative, simply add the really useful word just, as in 'Can I just borrow your pen for a second?' or 'Could I just interrupt for a moment?' (note the position of just in these two questions). Arguably, the main use of just is to mean 'a short time ago or before', as in ‘Susan was just telling me about your new job’ or ‘He had just arrived in Australia when the accident happened’. Then with the broad meaning of ‘only’, we have examples like ‘The medicine costs just a few pence to produce’ and ‘It was just a stupid mistake’.
Another meaning of just is ‘exactly’, as in ‘Thank you so much, it was just what I wanted’ or ‘He’s just like his father’. Mainly used in spoken English, although not exclusively so, just can also express strong emphasis, as in 'I just can't believe what's happened' or 'It was just awful seeing her so miserable'. Then there is the use of just in the broad category of ‘when something almost does not happen’, as in ‘The four girls just managed to squeeze into the back of Rick’s car’, 'He passed the exam but only just' and 'We should just catch the train if we run'. Finally, in an embarrassing situation when you find it necessary to explain your reaction to something, you might find the expression ‘it’s just that’ a useful one, e.g. ‘Can you lend me £20?’ ‘Well, it’s just that I’m a bit short myself at the moment’.