You can invest in funds through several channels. The simplest way is to contact the provider of the fund you want to buy, by telephone, on the internet, or by returning the tear-off sheets from advertisements published in the financial pages of the newspapers.
However, most people should take advice before investing. There are two ways to do that - you can either talk to a tied salesman for one of the fund providers, or you can discuss your investment plans with an independent financial adviser.
The third way to invest is through a funds supermarket or discount broker. A large number of these can be accessed via the internet (try entering "funds supermarkets" into a search engine).