
Yes - as Brainless said -if the amount you are expected to earn from your current wages will be above the amount of your tax allowance then the excess is divided into the appropriate number of weeks/months and deducted at each pay period.
So as a very rough example if you were paid monthly and earnt £1000 per calendar month then your expected earnings for a year would be £12,000. If you take the £6741 allowance from your from £12,000 you get £5259 and this is the amount that you would pay tax on. The £5259 would be divided by 12 - for the 12 months - and you would pay tax on anything you earnt above £438.25 per month.
If you were not able to give your new employer the form showing your correct tax code when you first started working for them - P45? - your employer would have to put you on emergency tax which is a higher rate than normal and you would get the excess you have paid refunded to you once your employer has received the form telling them your correct tax code.
The above is a rough guide in a very simple form and there may be other allowances etc that will affect the rate of tax you pay - and of course tax matters are never very simple :-)