+ ed / ing

(1)The mountain (was covered) with snow.
"was covered" is the passive voice of a verb to be plus the past participle of "cover"Not the Active voice.It's in Simple past tense.
(2)The mountain covered with snow.
"covered with snow" is participle phrase, adjective phrase,
Words to describe it will be "snowy",ie,the snowy mountain.
Or;eg:-The mountain ,covered with snow, is called Mt.Everest.