It’s easier for some than others.
Some people are just naturally funny. They’ll talk about their journey from their house to their school/workplace/uni/whatever and manage to get people laughing until they cry. They’re the kind of people who can make not-funny jokes funny.
On the other hand, there are deadpanners. They say things in a matter-of-fact manner, stuff that really shouldn’t be funny but for some reason cracks people up. The upside of deadpanning is that if no one gets the joke, it’s just like a normal part of the conversation. But if these people try to actually make a joke, things might get awkward…
Some people have a sense of humour that takes some time to get used to and might be offensive to other people. Black humour, racist jokes, stuff like that.
There are also people who aren’t funny per se, but are funny because of the situation they’re in. Think of batman gardening, or Kuchiki Byakuya (from Bleach) making a weird seaweed mascot out of sand and thinking that the mascot is the epitome of elegance, or Lord Voldemort giving a tour in the museum to a bunch of hyperactive school kids.