You can click the down arrow when swapping and click "+" next to Auto Router to see which fee you will get charged. Generally, small amount gets the lowest fees 0.05% or 0.01% for stable coin swaps; large amount gets a combination of different fee pools.

As an LP, it depends on which LP range you provide and whether the range serves the current price. If the range you chose is not where the current price's concentration is, then you won't get any fees. The white paper explains this pretty well. https://uniswap.org/whitepaper-v3.pdf