Were the 18th century battles we see in films real? I find it very strange that they would use such a stupid battle tactic. Just wait for the enemy to fire, lose the first line of soldiers and then order your army to fire.

More can always be said, of course, but I commend to your attention the appropriate section of the FAQ, specifically the headers 'Why did European armies use Linear Tactics?' and 'Mechanics of Linear Tactics'.

Adding onto that section, a few more posts:

u/StoryWonker has an overview of the relevant factors;
u/dandan_noodles looks at the dimensions of combat;
and on the degree of risk and likelihood of lethality;
and in conjunction with u/PartyMoses, the relative risks of being in formation;
PartyMoses also covers the dimensions of combat;
also how the fighting should go, according to one contemporary theory;
and on a common idea, why the troops don't duck/get down/lie down/similar.