For me, support means not being alone in my experiences. Being able to share it and having another's presence. Supportive presence is a support.
Supportive presence would mean the person is present and allows me to be, is with me, kind of like holding my hand. As opposed to dismissing, invalidating, telling me not to feel the way I do, etc.
(Non-supportive presence is a whole different story....)

For the most part I have found most of my interactions, irl or here, supportive. I guess that's cuz I stay away from the non-supportive ones....yeah, that's one of the ways I pracice self-care.