1To melt or thaw: a solid becoming liquid or soft due to heat or reaction. Kanji choice can indicate nuance (e.g., 熔ける/鎔ける for metals; 解ける often for ice or snow).
夏の日差しでチョコレートがすぐに溶けた。
The chocolate melted quickly in the summer sun.
工場では高温で金属が溶けていく。
At the factory, metal is melted at high temperatures.
春になると雪が解ける。
When spring comes, the snow thaws.
2To dissolve (in a solvent): a substance mixing into a liquid and disappearing (e.g., sugar dissolving in water).
砂糖を入れるとすぐにコーヒーに溶けた。
When I added sugar, it dissolved immediately in the coffee.
塩は水に溶けやすい物質だ。
Salt is a substance that dissolves easily in water.