Regarding the Kanji:
冷 is for objects that are cold, such as drinks, food, or whatever object you can think of.
寒 applies to the temperature around you or the atmospheric
temperature, not to the temperature of concrete objects.
Also take into account user3856370's warning. 冷{れい} (rei) is not a word per se but it is usually a component of other words, whereas 寒{さむ}い (samui) is an actual word meaning cold (weather-wise).
If you want to use 冷 as an adjective, as opposed to 寒{さむ}い (samui), the word would be 冷{つめ}たい (tsumetai).
Compare both adjectives in the following sample sentences:
今日{きょう}は寒{さむ}い ! / (kyou wa samui! ) / It's cold today!
このビールは冷{つめ}たくて 美味{おい}しい ! / (kono biiru wa tsumetakute oishii! ) This beer is cold and tasty!