You will probably know that you have obviously missed the public issue deadline by a week so you'll have to buy shares on the open market.
The easiest and cheapest way to buy shares is probably through your bank otherwise open an account with an online broker like the
Share Centre, deposit some funds and away you go. Bear in mind that there will be commission and administration charges in all cases.
Why Royal Mail though? are you an investing or after making a quick buck? For the latter, the boat has probably sailed already. Many analysts are saying that the price will probably remain relatively stable but don't expect any stellar dividends
There are some more risky options available to you such as CFDs (contracts for difference) or spread bets where you basically speculate on a rise or fall in any given stock. A practical example is that you could have speculated on the rising price of these shares if you had some foresight during the public issue. Either way don't do this if you're averse to risk.