What tactics the armies used during post-medieval times?

The actual introduction of firearms caused very little change to take place in tactics. The biggest change was that archers and crossbowmen were replaced by arquebusiers who fired in (usually) double ranks.

As firearms became more reliable (and usable in the rain) the pike was slowly replaced with more and more units firing various forms of firearm.

The largest change brought about by the advent of firearms was that armor became a handicap instead of a bonus on the battlefield. As firearms had no problem (usually) piercing armor, the weight and cost of that armor became a liability and was therefore almost abandoned until the twentieth century (the tank and armored cars).

The basic pike principle was used when Muskets came into the picture.

If you see on tv soldiers marching drills around with Guns that marchingis based on pike drilllook up the vatican guard you see their pike dril?l that is what modern marching (with guns)is based on.

Well thats where military drill comes from where they march with guns.

Onother adaptation to the extreme inaccuracy of the muskets was to use many soldiers. They would get a whole bunch of soldiers and fire en mass at an enemy army.

The principle was if lots of musket volleys where shot one of the inaccurate vollies had to hit someone eventually. Instead of having 5 people fighting 5 people with crappy muskets chances are the muskets would fail and neither side wold win.

That is one way their militaries adapted during the post medieval period.

Good Luck!!!

Nope tactics did not change a whole lot until the invention of the machine gun and WW1. Tactics only changed then because the British where running out of troops for the Germans slaughter by frontally assaulting machine guns. The introduction of combat aircraft at this time also forced change.