坐 is a vivid picture: two people (人人) sitting on the earth (土), facing each other — exactly what 'to sit' looks like. The character hasn't lost that little scene in 3,000 years.
坐 means 'to sit' — 请坐 (please sit / have a seat) is everyday courtesy you'll hear the moment you visit anyone. But 坐 has a second job: 'to travel BY' a vehicle, because you sit in it — 坐车 (take a car/bus), 坐飞机 (take a plane, 'sit a flying-machine'), 坐船 (go by boat). So when a Chinese friend asks 你坐什么来? they mean 'How did you get here?'.
Two people (人人) on the ground (土), facing each other — to SIT.
坐 also means 'to take' a vehicle — because you sit in it: 坐车 (by car), 坐飞机 (by plane). 你坐什么来? = 'How did you get here?'