This implies you have a folder/directory called 'celsiustofahrenheit' and it contains your 'CelsiusToFahrenheit.java' file in it.
Packages organize classes into a hierarchy of related subsystems. In Java classes are placed in specific directories called packages.
A quick solution is you should be able to remove the package line from your source (for simplistic one classs applications.) Packages are best used when you have an application that is calling many support classes.
For example, you may have a file structure like:
com\yourname\convert
com\yourname\converters
Your main application/class (call it 'Convert.java') may reside in 'com\yourname\convert' and would contain a
package com.yourname.convert;
line. If you then call a class called 'CelsiusToFahrenheit.class' which resides in the 'com\yourname\converters' folder, you would then include (in the 'Convert.java' source,) an
import com.yourname.converters.*;
line. This is so the compiler can find the 'CelsiusToFahrenheit.class'.
Of course your 'CelsiusToFahrenheit.java' source has a
package com.yourname.converters;
line