Not really.

[zhengl_2000]

The Americans use this phrase a lot.
but I am not sure how to use it .

For instance:
A: Are you tired or something?
B: Not really.

Here "Not really" means "not at all" or " I am just a little tired."

 

[Francois]

It more or less means 'nothing out of the way'.
You might be a bit tired but no more than usual.
At least it's not a matter of concern or complaint.

FRC

 

[Casiopea]

The Americans use this phrase a lot.
but I am not sure how to use it .

For instance:
A: Are you tired or something?
B: Not really.

Here "Not really" means "not at all" or " I am just a little tired."

To me, not really means something like, Truthfully? No or Technically? Yes. But....

A: Are you tired?
B: Not really. (i.e. Truthfully? No. I'm not really tired. I'm just bored.)

A: Do you love me?
B: Not really. (i.e. Truthfully? No. I do not really love you.)

A: Are you married?
B: Not really. (i.e. Technically? Yes. But I'm not really married; I'm separated.)