English has three forms of future, out of which only one is real future tense, the other two are present continuous with an auxiliary verb and present continuous without an auxiliary verb. id est: I will wite to you tomorrow. I am going to write to you tomorrow. I am writing to you tomorrow. Spanish has exactly the same three forms of future. Te escribiré mañana. Voy a escribirte mañana. Te estoy escribiendo mañana. Note only that, in the case of the second "I am going to", Spanish uses "I go to...". European Spanish favours the first "escribiré", whereas American Spanish uses the second a lot more often than in Spain. The third one is the least common in Spanish. Now, as for the second form "I am going to" "voy a", there is a question whether it should be used with the verb "to go", meaning "can you say "I am going to go"... in Spanish we can say "voy a ir a comer" and "voy a comer", both of which are widely accepted, having exactly the same meaning. I hope this helps.