You use though to introduce a statement in a subordinate clause which contrasts with the statement in the main clause.

You often use though to introduce a fact which you regard as less important than the fact in the main clause.

Though the weather was FREEZING, they set out on their hike with unwavering determination." （天候は凍えるほど寒かったが、彼らは揺るぎない決意でハイキングに出発した。）

Though he tried hard, nothing changed.（尽力したが、徒労に終わった）