The bullets were spherical lead balls (picture) contained in a paper cartridge which also held the black powder (gunpowder) propellant. The balls were smaller than the bore, wrapped in a loosely fitting paper patch which formed the upper part of the cartridge.
The lower part of the cartridge contained the gunpowder and the two sections were separated with one's teeth. The gunpowder was loaded first, followed by the paper from the lower section of cartridge as wadding. Then the ball and upper piece of cartridge were loaded. Finally, a ramrod was used to compact the ball and wadding down onto the gunpowder.
In flintlocks, the pan was either filled from a powder flask after loading the ball, or from the paper cartridge before the bulk of the gunpowder was poured down the barrel. Following its invention in 1807, muskets started to be fitted with percussion caps which were much more reliable than flintlocks, as well as working in the rain.
A very experienced user could load and fire at a maximum rate of around 4 shots per minute, but the average soldier was expected to be able to fire 3 rounds per minute.
Muskets were slow to reload and inaccurate, so army formations typically deployed musket-men in formations two or three lines deep. The first line would fire in unison, then drop to their knees to reload, while the lines behind them fired.
Owing to the musket's inaccuracy, musketmen were not expected to aim at particular targets. Rather, the objective was to deliver a mass of musket balls into the enemy line. Soldiers expected to face musket fire were disciplined to move in precise formations and obey orders unquestioningly. British troops in particular were reputed to be drilled until they could perform coolly and automatically in the heat of combat.