Learn Icelandic: Ert þú að gráta?

To say an action is happening right now, Icelandic uses the verb vera (to be) plus the word að and the infinitive (dictionary form) of the main verb. Here, ert is the conjugated form of vera for 'you', and að gráta provides the ongoing action.

Why does the verb Ert come before the pronoun þú?

Just like in English, Icelandic swaps the verb and the subject to turn a statement into a yes/no question. The statement 'You are crying' is Þú ert að gráta. Moving the verb to the front makes it the question Ert þú að gráta?.

Why isn't the verb gráta conjugated to match þú?

Because it is part of the vera að pattern! In this structure, only the helping verb vera (here as ert) changes to match the subject. The main action verb always stays in its infinitive (dictionary) form, which is gráta.

Could this sentence also translate to 'Do you cry?'

No, the vera að pattern is strictly for ongoing actions happening right now. To ask about a general habit like 'Do you cry?', you would use the simple present tense without að, which is Grætur þú?.