Just to add to the other answers:
A T shirt is called a T shirt for a very good reason - it is simple garment made in the shape of a letter T. It has a straight body, and two short arms. It doesn't open, and it has no fancy shaping, no buttons, no collar, no cuffs. Nothing else - just a T shape. You pull it on and off over your head. It's made out of soft cotton, the same as an undershirt.
A shirt is a more formal garment. Shirts have collars, buttons and cuffs. You put a shirt on by putting an arm in, pulling it round your back, putting in the other arm, then buttoning it up at the front. Men wear shirts under business suits for work.
A blouse is a woman's version of a shirt. At work, a woman might wear a blouse on her top half, and a skirt on her bottom half. A skirt covers you from the waist downwards. A dress covers the whole body - starting at the neck/shoulders and and covering at least some of the leg area.