Консультант сказал, что вы можете примерить джинсы и юбку.

Both words are in the accusative case because the verb примерить is transitive and takes direct objects.
• Джинсы is a plural noun. For inanimate nouns in Russian, the accusative form is the same as the nominative, so джинсы stays джинсы.
• Юбка is feminine singular. Its nominative ending -а changes to -у in the accusative, giving юбку.

Russian has two aspects for many verbs:
• Примерить is perfective. It describes a one-time, completed action (“to try on” once).
• Примерять is imperfective. It implies a repeated or ongoing action.
In a shop context you grant permission to try on the item a single time, so you choose the perfective примерить.

Russian distinguishes formal and informal “you.”
• Вы можете is the polite (or plural) form of “you can.” It’s used in formal contexts or when addressing more than one person.
• Ты можешь is the informal singular form, reserved for friends, family, or very close acquaintances. A consultant in a store will normally use вы to be polite.

Что introduces a subordinate clause in reported speech. The structure is:
[Main clause] , что [Subordinate clause]
Here, Консультант сказал is the main clause and что вы можете примерить джинсы и юбку is the subordinate clause explaining what was said.

In Russian, past-tense verbs agree in gender (and number) with their subject.
• For a male consultant: Консультант сказал.
• For a female consultant: Консультантка сказала (or консультант сказала if you still call her консультант).
• For plural consultants: Консультанты сказали.