A citizen would join a local pressure group to campaign on a specific issue that affects their local area. For example, they might join a group protesting against the building of a new road through a park because they want to protect their local green space and believe collective action is more effective than individual protest.
Pressure groups are organisations that try to influence government policy or public opinion on a particular issue. Citizens often join local pressure groups because they feel strongly about a specific local issue, such as opposing a new housing development, campaigning for better public transport, or protecting a local park. Joining a group amplifies their voice, provides resources, and creates a community of like-minded people, making their campaign more likely to succeed than if they acted alone.