Income tax
All workers in the UK must pay income tax. The amount you pay depends on how much you earn. Not all income is taxable. If you are on a very low wage and do not work full time you may not have to pay tax. If you are employed your tax will be taken via PAYE (pay as you earn) and will be deducted each month from your gross salary. The government's website has detailed information on a beginner's guide to tax and working and paying tax.
The UK has double taxation treaties, that is, an individual may receive income from one source but be resident in another and may be liable to pay tax in both countries under their tax laws. The UK has negotiated with more than 100 countries so tax doesn't have to be paid twice. Individuals must apply for the right to do this (it not automatic).
The UK government offer certain tax benefits and credits depending on your working status. Check on their website for more details.