More about I am doing or I do...

I cook/I'm cooking         He does/He's doing          It melts/It's melting      She chats/She is chatting
                  You're not going/ You don't go            We don't study/We aren't studying
                                                  They aren't leaving/They leave

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A. Study this explanation and compare the examples

Present Continuous/ I am doing Use the Present Continuous to talk about something which is happening at around the time of speaking:   ______________I am doing  ______________ past                       now                          future The kettle is boiling. Can you turn it off, please? Listen to those people. What language are they speaking? 'Where's Tom?    'He's playing tennis. (you find a stranger in your room) What are you doing here? Use the Present Continuous for a temporary situation I'm living with some friends until I find a flat. That machine isn't working. It broke down this morning.

Present Simple/I do Use the Present Simple to talk about things in general or things which happen repeatedly.  _______________ I do___________________  past         <------   now  ------>              future  Water boils at 100 degrees Celsius. Excuse me, do you speak English? Tom plays tennis every Saturday.  (asking people's job)  What do you do? Use the Present Simple for a permanent situation. My parents live in London. They have been there for 20 years. That machine doesn't work. It hasn't worked for years.

B. Some verbs are used only in simple tenses. For example you cannot say 'I'm knowing'. You can only say I know. Here is a list of verbs which are not normally used in continuous tenses. (but there are exceptions):

want        need   prefer      like    hate    belong       see    hear   know    realize    believe    mean

suppose     understand     remember    forget    seem   have(= means possess)   think (= believe)

            - Do you like pizza? (not 'are you liking?')

            - He doesn't understand it. (not 'He isn't understanding')

            - These shoes belong to me. (not 'are belonging')

            -  What do you think Josh will do? (= What do you believe  he will do?)

   but    - What are you thinking about? (=What is going on in your mind?)

[Reference:Murphy, Raymond (1985) English Grammar in Use, Cambridge, Cambridge University Press]