The three metro lines
Prague's metro has three lines, conventionally shown as green (A), yellow (B) and red (C), crossing at a few central interchange stations. Line A is the one most visitors use most, running through the centre and out towards the airport-connecting bus. Trains are frequent, clean and easy to navigate even without Czech.
Trams: the scenic option
Trams cover the parts of the city the metro doesn't, and they're often the more pleasant way to travel — several routes cross the river or skirt the castle hill with proper views along the way. Night trams keep the whole network running after the metro closes for the night.
How tickets actually work
Prague's public transport uses a single integrated ticket across metro, tram and bus, sold as a block of time rather than a single ride — typically a short basic ticket (around 30 minutes) and a longer one (around 90 minutes) that allows transfers. Buy tickets from machines at metro stations or tram stops, from the transport authority's app, or from some newsagents, and validate (stamp) a paper ticket the moment you board or enter the metro barrier — an unvalidated ticket isn't a valid ticket. Multi-day passes are worth it if you're moving around a lot.
Plain-clothes inspectors do check tickets and issue on-the-spot fines for anyone without a validated one, tourists included, so don't skip this step.
When to just walk
The historic centre — Old Town, Charles Bridge, Malá Strana — is genuinely compact and largely closed to general traffic, so for short hops between the big sights, walking is often faster than working out a tram connection. Save the tram and metro network for crossing the river district-to-district, reaching the castle from a distance, or getting out to areas like Vinohrady or Žižkov.