How did the British and French train their troops during the colonial eras?

Most jobs in those days, farm and factory work, was nearly as dangerous as the military.In the military, young men at least got a uniform, more or less enough to eat, and a place to sleep, which was more than many migrant farm or factory workers could count on. And a few were attracted by opportunities for travel and adventure and plunder.

Battles were bloody when fought, but fortunately few and far between. As to training, it helped that most men of the time (other than officers) were illiterate, and could be drilled relentlessly to march and shoot without thinking, and be "numb" to the death around them.

In typical European armies, troops were trained on a conscription basis. The training is a mix of the general background of the soldiers and what was expected of them in a battle. However, there were also volunteer armies and large-scale mercenaries, but mostly we're talking conscription.

In a European conscription army, men would be called or pressed into service largely at random, willingly or unwillingly, and particularly from the lower classes. For an unpopular war or service (like a navy), conscription gangs that would grab whomever they could. A popular war may see a lot of volunteers, though. Those from the upper classes/nobility would usually have an out or buy a commission and be an officer.

Because it was conscription and because there was usually war already at hand, training would be short and simple. Everyone walk together, move at the same time, fire at the same time, etc. In 17th and 18th century war theory, a massed group was viewed as the most effective presentation of force and fire, because most battle was with edged weapons. Muskets existed but were overrated, as mentioned in other posts. The bayonet was seen as the ultimate “battlefield sweeper,” and only a massed group can do it with the required effect. It wasn’t until the American Civil War that the bayonet charge was shown to be very risky to the charger, and in WWI it was suicidal.

Military training seeks to create a desired response in the soldier when exposed to combat. Even today military training seems harsh and simplistic and repetitive and it is (and I’ve been through it in my service), it is on purpose because those actions need to become the soldier’s automatic behavior when really bad stuff starts to happen around him. In the age we’re talking about, the soldier needed to stay in line and do what the officer told them. The officer often felt free to shoot/stab soldiers who didn’t do the right thing because they needed to assert their authority over the situation to overcome the battle.

It is CRITICAL in battle (then and now) that everyone does what they are supposed to do. If someone doesn’t, then things start to fall apart. Because lives and nations are on the line, you get draconian rules to ensure everyone does what they are supposed to do.

So, if you are standing in a regimental line with bayonet attached, you were probably pressed into service, had a brief military course and are doing what everyone else is doing because the officer behind you is calling the shots and will shoot you too if you don’t behave. Also, the 17th and 18th century army is likely operating without much support so you are probably very hungry, cold and getting sick. You’ll ravage local farms as you march by for food and warmth. In those times, when an army came through your village – even your own army – you’d probably lose your food and some possessions.

As mentioned in other posts, the kill rate in 17th and 18th century fighting wasn’t as bad as Hollywood makes it to be. Disease was a worse killer than bullets or edged weapons. Morale and not breaking and running was a very important part of the formula, as mentioned by @pugsville. When the shrapnel and bullet kill rate eclipsed that of edged weapons and disease, things began to change into modern warfare.