The present progressive or present continuous has these names because its primary use is to express activities which are “in progress” right now and which “continue” over time.
A. Right now I'm working in the garden.
In this use the construction contrasts with the simple present, which is used to express two different sorts of actions:
B. I work on my garden every weekend. ... expresses an activity which you perform habitually or repeatedly, whether or not you are performing it right now
C. I work for a software company. ... expresses a state which endures over time
Stative verbs like know, own and love are therefore not usually cast in the continuous form:
D. ✲I am knowing what to do. ✲I am owning a ’57 Chevy.
But with a non-stative verb like work it is acceptable (but not obligatory) to employ the continuous form with habitual/stative senses like those in B and C above if you are contrasting the present habit or state with a past or future habit or state:
B2. These days I'm working/I work on my garden every weekend (but I expect I will stop when the weather gets cold).
C2. I used to be a starving artist, but I work/I'm working for a software company now.
It is also employed when complaining about someone's habit or state, implying that the habit or state could or should be ended:
E. You're always working on your damn garden when you could be talking to me!
By and large, then, the present continuous expresses an impermanent activity or state which the subject is currently engaged in or “in the middle of”.
Accordingly, have is not ordinarily used in the present continuous when it is expresses ownership (which is a state); but it may be used in that form in other senses which imply activity:
F. ✲I'm having a wife and son. ✲I'm having a First Folio.
G. I'll call back later, I'm having my lunch right now. I'm having problems with this client.
A secondary use of the present continuous is to express an expected future activity. In this use it doesn't exactly contrast with the simple present; rather, it has largely replaced the simple present:
H. Today I'm at the office; tomorrow I'm working in my garden.