Turn-based tactics are games about squads and individual battles: you and your opponent take turns moving soldiers, seeking cover, flanking, and using abilities. Every decision matters, and a mistake can cost a soldier their life. The benchmarks of the genre include XCOM, Jagged Alliance, and Into the Breach.
The turn-based strategy covers economics, development, and the entire world map. Tactics focus on combat: positioning, cover, and every shot.
Isn't it too difficult for a beginner?The first missions usually teach the basics, and the difficulty can be lowered. A good start is Into the Breach: short fights and clear rules.
Any of these games can be downloaded via torrent, repack, portable version, or GOG release.