We form the present continuous with am/is/are + the -ing form of the verb.
The short forms of am/is/are are ‘m/’s/’re.
The negative short forms of am not/is not/are not are ‘m not/isn’t/aren’t.
Note that we can use short forms only in negative short answers, but not in positive short answers.
We use the present continuous for things happening now, at the moment of speaking.
We use the present continuous for temporary things that are happening around now (=not at the moment of speaking but these days, or weeks, etc.)
We use the present continuous with time expressions that mean ‘now’ or ‘around now’: now, at the moment, at present, today, these days, this week, etc.