On the original 1998 soundtrack for 'Mulan' you'll find the handful of big vocal numbers that everyone hums a decade later, plus the sweeping Jerry Goldsmith score underneath. The main songs from the film are: 'Honor to Us All', 'Reflection' (the film version sung by Lea Salonga), 'I'll Make a Man Out of You', and 'A Girl Worth Fighting For'. Those are the emotional and showy moments that anchor the movie, written by Matthew Wilder (music) and David Zippel (lyrics).
If you picked up the commercial soundtrack back then, you probably also remember the pop single: Christina Aguilera's studio version of 'Reflection' was released to promote the movie and got a ton of radio play. The rest of the CD is largely Goldsmith's score — battle cues, tender themes, and instrumental transitions — so if you love the orchestral side, the soundtrack gives you that cinematic sweep as well. Some editions and re-releases include extra score tracks or suites that expand on the motifs.
Fun little detail: when people talk about the soundtrack they often split it into the vocal highlights (the four big songs) and the score. If you're hunting for a specific track, the Disney soundtrack listing or a streaming service will show the vocal tracks at the top and then the score cues. And if you meant the 2020 live-action 'Mulan' — that movie left most musical numbers behind, but it had a new promotional song, 'Loyal Brave True' by Christina Aguilera, while the rest is mostly score-led.