The hard part is starting to forge and getting your first finished product. Since you’ve done that you can only get better at forging. As a couple people mentioned earlier feel free to stop forging at any point and make a post here with any questions. You can stop a forge midway and wont lose progress.
Typically this is exactly what you want. If you mean the large boon points bar on the left that means you got a good roll and all points went into one of your boons. If you mean the yellow bar in one of the 3 boon boxes, the bar going from full to looking almost empty likely means your boon went up to the next level, which is also what you want.
The only times you want to stop a forge is if you’re low on stability/vigour, if you already have rank 4 aoe (rank 5 aoe is random hit and is a bad boon), or if you’re about to get a quirk/defect you dont want. (These are harder to predict and where you decide if you want to take a chance or not) But make sure you deconstruct any tools with bad boons/quirks/defects instead of minting them.
And also remember if you have aoe on a tool, damage will always go down (damage gets spread across all blocks that tool hits). To negate this you just have to put the damage boon high enough to compensate damage loss from aoe.
Keep forging, you’ll be a pro in no time