1. Usage of 着（zhe）：着 follows a verb mostly, .sometimes follows an adj. eg.1 唱着歌(to be singing a song) eg.2 低着头 2. Meaning of 着（zhe)：着 doesn't has a substantive meaning itself, but indicate a continuous process of an action of the verb coming before 着，or indicate a status described by the preceding adj.. 3. When there are two verbs in a sentence describing a major action and its accompanying action, 着 goes after the accompanying one. eg.1 听着歌跑步 4. Difference of With 着 and Without 着： eg. 挂一幅画 put a painting on spl. 挂着一幅画 there is a painting hanging on spl.

“他笑着说不可以”------这句话完全正确

The translation for this sentence is " He said no, (while) laughing". "Verb+着" stresses an action that is/was ongoing at the moment.