The PRESENT TENSE indicates that an action is present, now, relative to the speaker or writer. Generally, it is used to describe actions that are factual or habitual -- things that occur in the present but that are not necessarily happening right now: "It rains a lot in Portland" is a kind of timeless statement. Compare that to the present progressive -- "Itis raining in Portland" -- which means that something is, in fact, going on right now. "I use my bike to get around town." is in the present, but I'm not actually on my bike right now. An instantaneous sense of the present can be conveyed with either the simple present or the progressive: "Watch him now: he holds [is holding] down the control key at the same time that he presses [is pressing] the letter d.