Bag of Holding-open for items?

I just bought a bag of holdings. How do I transfer items to it?

It’s a passive item which gives you more carrying capacity. No micromanagement needed.

To be slightly more specific on how it works. They have negative weight. -100lb (small) or -200lb (regular). You can see this by hovering over item or right-clicking on it.

Kinda ironic that Bags of Holding can’t actually “hold” anything, right? It’s more accurate to think of them as expandable backpacks for your standard shared stash.