Подойти is not future, it is an infinitive. The future form will be подойду (я подойду, он подойдет...). It means I will approach (or maybe come to your place, come to see you) and I am certain about it. Я подойду завтра - you promise to come. While the future form of подходить is буду подходить, it means the process. It can be used, for example "Когда я буду подходить к дому, я позвоню" - "When approaching the house, I will call you"
In present it is "подхожу" - I am approaching, I am coming
Past form will be "подошёл" (have come) or " подходил" (when we came the train was approaching the station - когда мы пришли, поезд уже подходил (it hasn't stopped yet)