"The thing is cold."
It is not easy to give a short answer for this, so to start, I would just advice you to remember to use 춥다 for the weather as in 요즘 날씨가 춥다 (the weather is cold these days). For things that "feel" cold, I would suggest to use 차갑다.
물건 is object/thing 것 has a similar meaning. Usually, it comes with three combinations: 1. 이것 this thing (right infront of you) 2. 그것 that thing (not too far away from you) 3. 저것 that thing over there (very far away from you)
As usual, we need to add subject or topic particles (이/가 or 은/는) after (이/그/저)것.
이것은 사과입니다. This is an apple.
저것이 바나나입니다. That thing over there is banana.
Not sure if I'm right or not, still a beginner here. Please correct me! Hope it helps