open
The Italian word 'aperto' is used much like the English equivalent 'open'. It is utilized in contexts where something is not closed or confined, it can refer both to physical spaces and abstract concepts. For example, a door can be 'aperto', or a mind can be 'aperto' (open-minded).
The shop is open.
The phrase 'Il negozio è aperto.' is a simple statement. It uses the verb 'è' (is) in the third person singular form of the verb to be 'essere', and 'aperto' as the adjective describing the condition of the shop.
I left the window open.
The phrase 'Ho lasciato la finestra aperta.' is a sentence in the past, more specifically this form is known as 'passato prossimo'. It describes an action completed in the past where I ('Ho') left ('lasciato') the window ('la finestra') open ('aperta').
The museum will be open tomorrow.
The sentence 'Il museo sarà aperto domani.' is a forecast about the future. It uses the future form of the verb 'will be' which translates to 'sarà' in Italian, and 'aperto' to describe the predicted status of the museum.