First of all, thanks for playing the game and for taking the time to share your feedback!
At the start, you can't use the pouch during a raid. Just collect the loot you find, and if you successfully complete the raid, you can move those items out/into the pouch afterward.
The game is meant to be a hardcore roguelite, so dying is part of the progression loop. Even if you can't beat the boss yet, killing regular enemies still gives you experience, so you're still making progress by leveling up.
There are also a few mechanics that can help, like the dice rolls at the Quartermaster, where you can try your luck to maybe gain some gold and buy better equipment. Once you get a few successful runs and gain some levels, the early raids become much more manageable.
Thanks again for giving the game a chance, and I hope this clears things up a bit. If anything still feels confusing or frustrating, I'd love to hear your thoughts so I can keep improving the experience and add more content or mechanics.