Test-Cheatcodes-Explain

  vm.expectRevert();

This said that the next line should revert (fails).

address USER = makeAddr("user");

This line make, returns an address for the person "user".

uint256 constant STARTING_BALANCE = 10 ether;
vm.deal(USER, STARTING_BALANCE)

This gives to the address of "user" the amount that you pass in ether, in this case it is 10 ether.

vm.prank(USER);

The next rtansaction will be send by USER.

uint256 gasStart = gasleft();
vm.txGasPrice(GAS_PRICE);

txGasPrice returns the transaction gas price and you must to pass the current gasprice.

vm.hoax(address, value)

This is a combination of makeAddr and deal.

        vm.startPrank(fundMe.getOwner());
        (transaction)
        vm.stopPrank();

This make that the transaction that you put into the vm.Stop and Start Prank, will be send by the address that you pass.

assert(1 == 1)
assertEq(1, 1)

this check if the first thing that you pass is equal to the second.