to arrive
The Italian verb 'arrivare' means 'to arrive'. It is commonly used just like its English counterpart to indicate reaching a destination. For example, 'Arriverò a casa alle otto' translates to 'I will arrive home at eight.' Note that, like other Italian verbs, 'arrivare' changes its form based on the subject and tense.
When you arrive home, call me.
In this sentence, 'arrivate' is the second person plural present indicative form of 'arrivare'. It is used in a context where the speaker asks someone (or some people) to call him/her once they arrive home.
I am arriving at the station.
Here, 'Sto arrivando' is a present continuous tense form of the verb 'arrivare'. By using this form, the speaker indicates an action that is occurring at the moment of speaking.
I cannot believe that you have finally arrived!
In this case, 'arrivato' is the masculine singular past participle form of 'arrivare'. The conjugation of this verb in the past participle form is commonly used in the formation of the compound tenses.