I am a new DM, trying to understand the magic of the Portable Hole. I've read through as many previous posts on Portable Hole shenanigans as I could, but none seem to answer my questions. One of my players has managed to find a Portable Hole, thanks to the random loot tables. He's familiar with them due to having played earlier versions of D&D. I, having never played these versions, am not as familiar. We find ourselves at odds on just how this item works. In order to keep this post short, I won't post my interpretation of the rules, though suffice to say I disagree with the following.
The Portable Hole can be opened by two people, holding it open like a sheet.
If even the smallest portion of the cloth is opened, the portal is opened and the character can reach into the extra dimensional space.
The Portable Hole can be thrown upwards, and unfold on its way back down, therefore opening the portal.
Do the rules shed any light on these complicated questions?
RAW rules indicate the negative for all of those possibilities
No, it can not. The portable hole(DMG, 185) states with my emphasis:
Only one person can open the portable hole, whoever has it must use their action. It's also important to note that the second part of the sentence dictates that the extradimensional space doesn't open until it's been unfolded and placed on or against the surface.
This question also suggests a means of opening the hole that isn't listed in the description. The only RAW way to use the portable hole is for a single character to use their action to unfold it completely on or against a solid surface.
For your final question, please refer back to the original quote on the portable hole mechanics in that the item must be placed on or against a solid surface. Throwing it up in the air is not placing it on or against a surface. Yeah, it'll eventually maybe fall down and land on one, but that's not placing it. It also doesn't turn into the access to the extradimensional plane until it's unfolded and on or against the surface.
A note on clever uses
None of the above means the players can't figure out ways to be clever with this - it just means they need to try and be clever within the constraints of how to use it.
Of course, you as DM may opt for more freedom in how to use it, but if you're asking about the RAW constraints, these are what we've got.