Trying to learn a song in the first week hits a wall, because a song is several skills at once: chord shapes, changing between them, strumming and timing. The first thing to learn is smaller: one clean chord, held so every string rings. It will also make your fingertips sore, which is normal.
Your first day
Tune the guitar with a free phone tuner app first. From thickest to thinnest the strings should read E, A, D, G, B, E.
Then learn E minor, the fastest chord to get clean: it needs only two fingers, and every string is played, so a buzz has nowhere to hide. Put your middle finger on the second-thickest string at the second fret and your ring finger on the third-thickest string at the second fret. Frets are the metal bars along the neck, counted from the tuning pegs. Press just behind the metal fret, not on top of it, then strum all six strings slowly downward with your thumb or a pick, four times.
Lift both fingers fully off, reset the chord from scratch and repeat. You're done when you can put the shape down and hear all six strings ring without a buzz. If one buzzes, press closer to the fret before moving the finger, since a buzz usually means the pressure is in the wrong place and not that your fingers are.
The thing most people miss
Sore fingertips in the first weeks are skin toughening into calluses, which usually takes a few weeks of regular playing. It doesn't mean your technique is wrong, and it fades on its own. Sharp pain in a wrist or joint is different: stop and check your posture.
Short, frequent sessions are usually easier on sore fingertips than one long one. Ten minutes a day beats an hour on the weekend.
What not to buy
Don't buy a capo or extra picks yet. The free phone tuner is all you need, and staying in tune matters more than any accessory, since an out-of-tune guitar makes even a correctly fingered chord sound wrong.
Once Em rings clean, add A minor, which uses the same fingers moved down one string plus your index finger on the second-thinnest string, and practise switching between the two slowly. Changing chords without stopping is the skill most songs are built on.