The present continuous tense is also known as the present progressive tense.  In English grammar, verb tenses are categorized according to present, future and past tenses, with sub-categories: simple, continuous and perfect continuous.

Present Continuous

am/is/are + present participle

The simple present and the present continuous tense are sometimes used interchangeably in English grammar, the present continuous emphasizes the continuing nature of an act, event, or condition.

The on-going nature of the action is emphasized by the use of the present continuous rather than the simple present:

Jane is looking for her brown boots.

The present continuous tense can be used to refer to a future event when used in conjunction with an adverb or adverbial phrase:

The stadium gates are opening in 10 minutes.

John is arriving on Tuesday.

The present continuous tense is used to talk about continuous activities: (At the time of speaking)

I am reading this page now.

As well as in a more general sense: (now/near future /longer actions in progress now)

I am learning English this year.

And it is used to talk about planned future activities:

Joe and Jean are coming to dinner tomorrow.

Non-continuous verbs cannot be used in any continuous tenses. Instead of using present continuous with these verbs, you must use simple present:

“She is loving this chocolate cake.” Not correct
“She loves this chocolate cake.” Correct

The present continuous tense,  used with words such as “always” or “constantly”, expresses the idea that something irritating or shocking often happens. Notice that the meaning is like simple present, but with negative emotion. Remember to put the words “always” or “constantly” between “be” and “verb-ing.”:

She is always coming to class late.

The on-going nature of the action is emphasized by the use of the present continuous rather than the simple present.