It depends on the gender and the ending of the word.
If it is masculine and ends in a consonant like стол (table) plural should be столы. If it ends with an й like музей (museum) plural should be музеи and if it ends with ь like словарь (dictionary) plural is словари.
If it is feminine and ends а like лампа (lamp), plural should be лампы. If it ends in я like наделя (week), plural is надели. If there is an и before the я like in история (history), the plural has two и being истории. Words that end with ь end in и as well, for example: ночь becomes ночи.
If the word is neuter and it ends with o like лицо (face), plural is лица. If it ends with е like море (sea), it becomes моря. If it ends with ие like здание (building), it becomes здания. And if it ends in мя like имя (Name), the plural is имена.
I hope this is helpful