Initially, (World War 2 years) - there were "Link Trainers"
Was the manner for pilots to learn to fly instruments.
But all the rest of training was made in airplanes.
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Back then, people learned in Tiger Moths, in Harvards... then went to Spitfires.
The airlines trained in the actual airplanes.
I recall first airline F/O assignments to be RHS on cargo C-47/DC-3s...
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I joined airlines in the late 1960s... the first simulators were crude.
Few had motion, and visual equipment.
I started as pilot trained as flight engineer in 727.
Even had to demonstrate manual gear extension in the airplane.
Then, later, as new 727 F/O, had to do a few "touch and goes" after "simulator" training.
Did it like that, for the 707 and the DC-8 as well.
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Then came the 1980s, with excellent simulators, motion and visual.
The "real airplane" was EASIER to handle than... these simulators.
My first trip as captain on the 747... was the first time I landed one.
Never had been a F/O or F/E on type.
Just had a check-captain with me, in the co-pilot seat... and 300 passengers.
The only seat I had experience with in the 747 was... the toilet seat.
After my 747 first landing (ever) was FRA... I said "is that all there is...?" -
And I think I recall the passengers clapping their hands.
Only the cabin crew knew
After some 25 hrs and 3 landings, the check-captain said "so long, go kill yourself...!"
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Happy contrails