Sufficiently means enough — but enough for a purpose, not enough in general. It sits in front of an adjective or an adverb (sufficiently large, sufficiently well) and it almost always looks forward to what the enough is for, either spelled out with to or for, or clearly understood: "She was sufficiently strong to lift it", "The wound had healed sufficiently for her to go home". Where enough follows the word it changes (strong enough), sufficiently goes in front (sufficiently strong) — that swap is the single thing learners get wrong most. It is noticeably formal: reports, instructions, science writing, careful speech. In ordinary conversation people say enough. It also carries a faint sense of a standard being met, of someone checking, which is why you find it in rules and test conditions. Used alone at the end of a clause it means "to the needed degree": "The plan was not explained sufficiently."