When you trade on PolyZap and interact with the Swap / AMM and Yield Farm features you will sometimes have to pay a fee or a transaction cost. It's important that you understand these are not the same thing.
A fee is a service charge from the Swap / AMM / Yield Farm, which depends on the feature you are interacting with. Such as trading on the Swap / AMM (0.25%), staking LP tokens in the Zap Farms, or staking other token types in the Zap pools.
If you are using the Swap / AMM all fees will be displayed in the summary modal window that is displayed to the user before processing the transaction. At this point the user can review the details of the Swap / AMM fees for the transaction before it happens. You then have a choice to Confirm or Cancel the operation.
If there is a fee for a Yield Farm service it will be clearly labeled and visible in the User Interface (UI), for example "Deposit Fee 2%". Likewise if there is no fee for a service it will still be labeled in the UI most of the time, to make sure it's totally clear. For example "Deposit Fee 0%".
PolyZap will never charge you a fee secretly, it should always be visible in the UI, and recorded in the projects documentation (that you are reading).
A transaction cost is a charge from the underlying network transport, i.e. the Polygon Network, for processing your wallet interactions with the Swap / AMM and Yield Farm features.
Technically, when you use the Swap / AMM and Yield Farm you are actually interacting with the Smart Contracts that are setup for each service.
An example is the Zap Farms - when you stake your PolyZap LPs in the farm, Harvest your PZAP or withdraw your PolyZap LPs, you will have to pay a transaction cost. The cost depends on the complexity of the Smart Contract process / logic, however you will always be able to review the proposed transaction and costs in advance, before approving it.
If you are using MetaMask - a transaction window should be displayed in your browser, every time a transaction has to be processed. See the screenshot below for reference.
Reject - you can always reject a transaction if you want to, at which point the transaction will be terminated and you will incur no costs. Also the operation that were attempting to carry out with the Swap / AMM or Yield Farm will also be cancelled.
Confirm - if you confirm the transaction then it will be submitted for processing on the network. For the transaction to complete it has to be confirmed on the network a number of times. Depending on network traffic and / or congestion this can be instant pretty much, or take a longer period of time to finalize / process.