Ethereum- Learn Solidity step by step

1. Common Function Types:

• public: Anyone can call this function,but it isn't really used for any type of security per se.

• private: Only contract can call this function.

• view: This function returns data and doesn't modify the contract's data.

• constant: the same function type as "view".

• pure: Function will not modify or not even read the contract's data.

• payable: We might attempt to call it and send money to the contract at the same time.

 Ex:
contract Indox{
String public message;
 *Function format
 function getMessage() public view returns (String){
 return message; }
} 

    2.What is Gas?:

• GasPrice: Amount of Wei the sender is willing to pay per unit gas to get this transaction processed

• StartGas/GasUnits: Units of gas that transaction can be consumed.