Enforcement varies from theoretical to genuinely strict depending on the country. At the relaxed end, sorting is encouraged but nobody checks. At the strict end, in parts of Europe and East Asia for example, collectors will refuse improperly sorted bags, some cities require official pre-paid bags or stickers, and repeat offenders can face real fines. A few systems even charge households by the volume of general waste they produce, which makes sorting a direct money-saver.
Beyond household rules, many countries now ban or tax single-use plastic bags, mandate deposits on bottles, and require special handling for electronics, batteries, and bulky items. Dumping furniture or appliances on the street without arranging official collection is fined almost everywhere that enforces anything, and illegal dumping penalties can be steep.
As a newcomer, the practical move is to check your municipality's official waste page for the rules and penalty schedule, and to ask your landlord what has caused problems in the building before. Compliance is rarely difficult once you know the system; it is the not-knowing phase where people get caught out.