A formal boot camp for marines started only in 1910 or so. I presume the army followed much the same pattern. Until then, recruits learned their duties on the job with the units. You were an infantryman, all your friends were infantrymen, everyone you saw around you did the same job as you.

Their tasks were simple and were engrained by endless repetition under the gaze of sergeants who learned the same jobs the same way.

Nowadays, most soldiers it seems have strange low-density jobs. I once had a tenor come through my basic training company. That was his job, tenor.

Men worked in groups are were not expected to show a lot of initiative. Officers did the thinking, and the men did the work. Soldiers of the period rarely mentioned their division or corps. Life was at the regimental level or lower.

WWI was a mess. The army had not thought out how to mobilize large units. There was lots of marching. If the equipment was available, there was lots of dry-firing. Units even had to use dummy guns and go bang-bang.

But US troops went overseas ill-trained and worse-equipped. Harry Truman's artillery unit was given French guns when they arrived and the officers were shipped off to learn how to use them. The US produced not a single airplane in time for the war. Our guys used British and French weapons, or US-made versions of everything more complex than a rifle.

This of course meant that their US technical training had to be redone when they arrived in France. US troops were initially not well thought-of. Later they got better.

So marching, physical fitness training, drill and ceremonies in the US and then the real training in France under foriegn officers.

I hope that helps.