Verb tenses: uses

Present Simple

Use the Present Simple to express the idea that an action is repeated or usual. The action can be a habit, a hobby, a daily event, a scheduled event or something that often happens. It can also be something a person often forgets or usually does not do.

Examples:

• I play tennis.
• She does not play tennis.
• Does he play tennis?
• The train leaves every morning at 8 AM.

Past Simple

Use the Past Simple to express the idea that an action started and finished at a specific time in the past. Sometimes, the speaker may not actually mention the specific time, but they do have one specific time in mind.

Examples:

• I saw a movie yesterday.
• Last year, I didn't travel to Korea.
• Did you have dinner last night?

Present Continuous

Use the Present Continuous with Normal Verbs to express the idea that something is happening now, at this very moment. It can also be used to show that something is not happening now.

Examples:

• You are learning English now.
• You are not swimming now.
• Are you sleeping?

"Going to"

"Be going to" expresses that something is a plan. It expresses the idea that a person intends to do something in the future. It does not matter whether the plan is realistic or not.

Examples:

• He is going to spend his vacation in Hawaii.
• A: When are we going to meet each other tonight?
  B: We are going to meet at 6 PM.
• I'm going to be an actor when I grow up.

Source:http://www.englishpage.com/verbpage/verbtenseintro.html