There are many types of bike, which are designed for different terrains or styles of riding.
Many people start cycling when they dig out an old bike or are given one, and in this instance, the one you have is probably a good place to start.
It's a good idea to check the type of bike you have, so you're aware of its strengths and weaknesses, and to make sure you're comfortable riding it – ie, you can straddle the crossbar and reach the handlebars.
Locks come in many different types and strengths, and it’s a good idea to spend at least £25-£30 for something decent, but you might have to spend much more (up to £100) if you have a bike that's very attractive to thieves and is valuable.
Beware that many cheaper cable locks can be cut through VERY EASILY, and it takes much heavier and more expensive cable and chain locks to make your bike less attractive to thieves.
D-locks are, in general, harder to cut through but cheap ones can can be easily broken in other ways, so buy something decent.
Usefully, D-locks can often be attached to your frame, so you don’t have to carry them around on your person or in a bag.
By law you must have a front white light and a red rear light when cycling at night.
There are different types on the market, many of which do the same job, although more expensive lights may be more powerful. Modern LED lights are fairly cheap, nice and bright, have long-lasting batteries, and can be put on and taken off quickly when you park.
All new bikes are sold with a bell, and though it's not a legal requirement to have one, they're useful for alerting cyclists and pedestrians to your presence.
People tend to appreciate an early, non-aggressive warning, especially if you're on a shared path and you're behind them: a couple of tings when you're still 10 metres or so away works well.
Puncture repair items and pump
Being able to fix a puncture on the move is very useful. Yes, you can walk to a bike shop or hop in a cab, but it's inconvenient or expensive.
Once you've learned, fixing a puncture takes just a few minutes, and you only need to carry lightweight and inexpensive items.
This page explains puncture repair, though it's often easier to learn when someone shows you face to face.
Why not contact your local group to ask about free or subsidised maintenance courses, or to find a friendly face willing to show you.