I agree about the explanations; I didn't have enough time for a proper explanation bc of work. I updated the description to explain the controls.
For the second level though (spoilers in case you want to retry it),
you can return to the first terminal and reset it to use less blocks, then you'll have more for the second bridge. There's no requirement that you must use all blocks for each bridge. The guideline in each terminal is just to remind you how large the space to cross is. (At least it usually is. I forgot to set those properly too.)
Having come back to the game after this, I managed to figure out the block system, and get a lot further into it. The block system, although a bit clunky to figure out at first, does work well for some open-ended puzzle solving, and making it so enemies give you block is a clever way to make a player have to engage in combat without making it feel too much like grinding. I will note, I did seem to come across one bug, which is when you die with a bridge built, that bridge remains there, and if you get more blocks from killing enemies and reset the prebuilt bridge, it gives you both sets of blocks. This makes it easy to theoretically build infinitely long bridges. Other than that, the game is decently well put-together, and I can see I was a bit hasty in my initial review of the game.
Thank you for the review! The pause menu in the bridge builder has some tooltips that explain some of this (again, I was rushing). The bug is partially intentional: it allows for the game to get progressively easier as the player dies more, but also requires the player to re-kill all the enemies to get more blocks, sacrificing time for difficulty. Definitely still a bug though: try to use too many blocks on a bridge and the game will freeze :)