Have you tried? I'd like to see your tryout code so I can check what's wrong.
Please save the code as code bit, and attach its link in post Description
Fell asleep it was late when I wrote my last response.
Use a for...loop to iterate the string. You can follow BroFar's path as in the example given
Use conditionals `if` or `switch` to verify whether the character was a vowel
If it was, add the character to the result string. Otherwise, ignore the character. You can then get the result string length as vowel counter. You can evade the need of additional string and simply use a counter variable also, it's all your choice.
Happy trying, and don't hesitate to ask along the way ...