Nobody is born knowing what a phono stage is. Like most hobbies, Hi-Fi buries a handful of simple ideas under vocabulary. This page is the map: the three jobs every system does, the words used for them, and which guide to read when you're ready for each part.
A system is three jobs
Music starts somewhere, gets louder, and becomes sound. That's all a system is. The first box is called a source: a streamer, a CD player, a turntable. The middle box is the amplifier, the engine, where the volume knob lives. The speakers are the only boxes actually making sound, which is why they deserve about half your budget and most of your attention. There is one optional fourth box, the subwoofer, which takes over the deepest bass when your speakers can't reach down that far.
If you're about to buy your first system, read What do I need for my first Hi-Fi system? It walks through the three boxes, the money split, and the one shortcut worth knowing: speakers with the amplifier already built in.
The words that get in the way
Line level. Phono stage. Impedance. DAC. Each is a small idea in a big word. A line-level signal is just one of normal strength. A DAC turns the numbers of digital music into an electrical signal, and you already own several. Impedance sounds like physics homework and matters for about one buying decision in a lifetime, which What does speaker impedance mean? untangles in five minutes.
The two guides worth reading early are What is a phono stage? and What is a DAC? They're short, and afterwards most spec sheets become readable.
The cables, briefly
Two families do nearly everything. Signal cables carry quiet music from source to amplifier. Speaker wire carries heavy current from amplifier to speakers; it is plain copper, it is cheap, and there is nothing to overthink. What cables do passive speakers need? is the complete shopping list.
When something hums
One day something will hum. That is almost never a broken amplifier; it's two devices disagreeing about earthing, and Why does my amplifier hum? has the ten-minute unplug test that finds the culprit.
The vinyl path
Turntables are the steepest part of the beginner curve because they're mechanical: a diamond tip rides a groove, and the wobble becomes music. That also means setup matters, and a badly set up record player damages records. When you get there, read Can I connect a turntable directly to my amplifier? first, then How do I set up a turntable?
Buying and growing
Used gear is where Hi-Fi value lives: a respected brand's amplifier from the 1990s routinely outlives new budget gear at the same price. How do I research a used Hi-Fi product? is the fifteen-minute routine, and this site's product pages do the lookup part for any model. Once a system exists, What should I upgrade first? keeps the next upgrade somewhere audible.
That's the whole map. Pick the guide that matches today's question; the rest will still be here when the next one shows up.