Well humans wear clothes for 3 main reasons:

1. Cover nakedness: Nobody wants to have to walk around with their privates on display to the world and although nudeism is actually a real live thing, it's not something that's widely accepted in the world.

2. Protection: Clothes keep the body warm and also protects us from harm. Imagine if you had to sit down in an air-conditioned office for hours everyday without any clothes on, or if you had to walk outside but naked on a snow day. Clothes shield us from direct sunlight and also protect our bodies from things like insects and spiders.

3. To look stylish/indicate a position or office: People wear clothes because they want to look good. Yes, an ordinary shirt and trouser will do the above two things that I've stated , but wearing a more stylish combo will be sure to make you look better and attract more stares. People also wear clothes to indicate what kind of job, rank or position that they occupy. How would you know if a person was in the army if they didn't wear their uniform.