Name is simply what you want to call your token, such as Bitcoin or Ethereum.

Symbol will be the ticker of your token, such as BTC or ETC (normally tokens have a 3 letter uppercase symbol).

Decimals is how many decimal places your token can have, which determines how divisible it is. Generally tokens will have 18 decimals, which allows 1 token to be divided into trillions of pieces (eg. with 18 decimals you could have as little as 0.000000000000000001 of a token).

Total Supply will be number of tokens available. Token Total Supply VALUE will be total number of tokens to the power of decimal places. (eg. if total supply is 1000 and decimals is 18 then actual value that will be sent to the contract would be 1000000000000000000000.)
Note: the multiplification is being done automatically so you don't have to do it manually.