Solidity provides conditional code execution with the help of the if...else instructions. The general structure of if...else is as follows:

if (this condition/expression is true) {
   Execute the instructions here
} 
else if (this condition/expression is true) {
   Execute the instructions here
} 
else {
   Execute the instructions here
}

if and if-else  are keywords in Solidity and they inform the compiler that they contain a decision control condition, for example, if (a > 10). Here, if contains a condition that can evaluate to either true or false.  If a > 10 evaluates to true then the code instructions that follow in the pair of double-brackets ({) and (}) should be executed.

else is also a keyword that provides an alternate path if none of the previous conditions are true. It also contains a decision control instruction...