What case do you use when you want to say you don't have something?

In Russian, when you want to say you don't have something you need to use the construction у меня нет + genitive case when talking in the present tense. For example, when your teacher asks if you have a dictionary and you don't, you need to say: у меня нет словаря. The nominative of dictionary is словарь (masculine) and the genitive is словаря. This works very similarly in the past tense. So if yesterday you didn't have a dictionary with you, you would need to say: Вчера, у меня не было словаря. Let's talk through a few more examples to make sure you understand and to check you know how to decline nouns in the genitive.