Here is an example of formal letter:
Scotland Travel Ltd.
99 Frederick Street
Edinburgh EH 1 PP
I intend to come to Scotland for a holiday in summer and I am particularly interested in Edinburgh and Aberdeen. I should be most grateful if you would send me some illustrated brochures of these two cities, as well as lists of recommended hotels.
Could you also let me know what reductions in railway fares, if any, are granted during the summer months?
I am looking forward to hearing from you soon.
[ your name]
I hope it helps.