If you are an adult and wish to take up chess, no matter what your standard, then the best way is to contact your nearest chess club, see the links on the right. Don't worry about how good you are. Clubs welcome players of any strength. Although most club players relish competitive chess, i.e. in the league and knock-out competitions, etc, described further on, you can just play 'friendlies' if you prefer.
Parents of juniors, players under 18 years of age, can also enquire whether their local club supports younger players. Juniors are sometimes better served by local schools, many of whom run chess activities. There is also the Hertfordshire Schools Chess Association, http://hertfordshireschoolschessassociation.com/, who will offer advice.
Alternatively, contact an officer in the HCA for general advice. Club fees are generally around £50 a year but they usually allow new players time to settle in a bit first. In addition membership of the English Chess Federation (ECF), http://www.englishchess.org.uk/, is required if you play regular competitive chess. Their fees start at £15 (juniors £11) per year. The ECF 'grade' games to arrive at your playing strength. After 10 games you obtain a grade, revised twice a year, that helps your club ensure you play at the right level.