Step-by-step explanation:
This is going to depend on the language you're working in heavily.
First you will want to verify your number is an integer rather than a floating point which will completely depend on the language and whether you care if the floating point is 1.0 for example, which could still be converted a valid integer value.
After you've determined if it is an integer you can use modulo to check if the integer is evenly divisible by 5. In C-like languages you would write this as `x % 5`. Any result other than zero would mean it is not evenly divisible.
You also need to check if the integer is >= 10 and <= 100.
Read up on for/while loops and break/continue in those loops to understand that concept, it is pretty universal to all languages.
Good luck!