Musical instruments of all kinds are divided into categories, or "families," depending on how they produce their tones. Instruments that make their sound when a player buzzes the lips into a long, twisted tube are called "brass instruments," even though they are not always made of brass. The standard instruments in the brass family have a range of timbres, pitch regions and playing styles. These instruments can be found playing together in large ensembles.
The trumpet is the smallest instrument in the standard brass family and the highest in pitch. In classical and jazz sections, trumpet parts are written to lead the rest of the brass family in style and interpretation. The trumpet sound is the easiest to hear and pick out of the section. The trumpet is a conical brass instrument, which means the bell flares dramatically and suddenly in shape, creating a piercing, forward-sounding tone.
The French is, in many ways, the most unusual brass instrument. Its tubing length is close to that of the tuba (the largest and lowest), but it has a small mouthpiece, suited for playing notes in the high range. This gives the instrument a very wide range. It is also the only instrument played with its bell facing backwards. It is also tuned to be a little too high in pitch (compared to standard tuning) to accommodate the effects of the player's hand held in the bell. The French horn is a cylindrical brass instrument; the gradual flare to the bell gives it a warm, wafting and ambient sound.
The trombone is a large conical brass instrument. Its sound would be similar to a low-pitched trumpet were it not for the effects of the slide. Where other instruments' pitches are (partly) controlled through valves that open or close off sections of tubing, the trombone is controlled by a slide that effectively makes the instrument longer or shorter. This gives the trombone a smooth, fluid and mellow sound on its note changes, as opposed to the crisp and sharp note changes on other instruments.
The tuba is the lowest pitched of the standard brass instruments, as well as the largest. It plays in the same range as the lowest part of the piano or other bass orchestral instruments (i.e., double bass or contrabassoon). It has a cylindrical brass shape that creates a low, booming sound that resonates deeply and widely throughout a room without cutting through the orchestra.
The euphonium and baritone are two different instruments, though they are similar and often confused. Both look and sound like a miniature tuba, though they play in the same mid-low range as the trombone. The difference is in their shape and the resultant sound; the baritone is conical and narrower while the euphonium is cylindrical and wide. The instruments are standard in concert bands and brass bands but rarely used in orchestras.