If I'm being completely bluntly honest, I'd prefer "Greg pulled a low bench from under a table". I agree with Cathleen that show v tell is frequently misunderstood. Unless the you have a reason for the stool to be making loud noises or tracks in the ground, I would just go with "Greg pulled a low bench from under the table".
Not only is telling fine, it's sometimes necessary. I generally choose one or the other based on how important it is to the story. For central events, characterisation, details etc, I'll show it. However for less important details, if you elaborate too much you'll go off on tangents and your story will be bogged down with unnecessary description. This then has a negative effect on pacing. (Though if you want to slow a story down in places because the pacing's too fast you can use this to your advantage as long as you keep it interesting.)
I'm concerned that this action you're trying to show rather than tell isn't important enough to require such a vivid description. If it is really important, as in what happens afterwards won't make sense unless this stool has been pulled out amid tracks in the ground/a loud noise, then choose the one that has the effect you need. If it's just an incidental thing he does (like maybe he pulls out the stool to stand on it and get something really important down off the shelf) then I'd just say plainly that he pulled out the stool and stood on it, and save my descriptive words for the important thing on the shelf.
Good tips: choose the right details. Also, it's common for fairly new writers to think that you have to describe every little action. You don't. For example:
Joe gripped the door handle, turned it, and pushed the door open. Then he walked through it. Then he walked across the room, opened the fridge and took out some bread (etc etc longwinded description of making a sandwich)
versus
Joe went into the kitchen and made himself a sandwich.
The first might be appropriate if Joe was recovering from a serious illness or injury that made doing all those movements difficult, so you'd want to emphasise that he's now well enough to do those things. For nearly every other situation, you'd just say he made a sandwich. You don't need to say that he opened the kitchen door, opened the fridge, got bread, filling, utensils etc, because all this is implied by "went into the kitchen and made himself a sandwich"
Last tip: there's loads of good advice out there, but almost none of it should be taken as rules. The advice is important but it has to be understood in context. There are always times when the advice doesn't apply. About the only thing I'd say always applies is "don't bore or confuse the reader" though what's boring is subjective and there's probably someone out there that's managed to make confusing the reader work artistically.