Fees are set as a "flat rate" per transaction, but normally expressed as a fraction of "price over size"

So if a fee is 150 "sat/byte" or satoshi's per byte. A satoshi is 0.00000001 of a bitcoin.

So if your transaction is 250 bytes (which is average for a single transaction to a single person), then you will pay (250 * 150) satoshis (37500 sat), which is about $5.

If your transaction is larger, you'll pay more, if it's smaller, you'll pay less.

But they are "ranked" in terms of who is picked first by "sat/byte" since the amount of room in the block is only 1MB.

So a 500 byte transaction with 37500 sats in fees is worth less than a 250 byte transaction with 37500 sats in fees, because the 500 byte transaction takes up more room that other higher paying transactions could fit in.