Unit Tests for spring boot application

I have never used JUnit testing before.I need to test my code with JUnit.
I have been searching google for all day but the problem is that I found examples using Mockito but in my code I didn't use dependency injections(@Autowired).
How can i use it for these methods?

Thanks in advance.

public class WordService {

public WordService() {
	
}


public static String upperCaseFirst(String value) {
    char[] listChar = value.toCharArray();
    listChar[0] = Character.toUpperCase(listChar[0]);
    return new String(listChar);
}

/**
 * Find and return the search word
 * @param name
 * @return the word sought or null if not found
 */
public Word findWordByName(String name){
	
	String nameUpper = upperCaseFirst(name);
	
	WordDao w = new WordDao();
	Word found = w.findWord(nameUpper);
	
	List<String> definitions = new ArrayList<>();
	
	if(found != null) {
		for(int i=0; i<found.getDefinition().size(); i++) {
			StringBuffer defBuffer = new StringBuffer();
			
			String definitionFound = found.getDefinition().get(i);
			definitionFound = definitionFound.replace("\n", "");
			
			defBuffer.append(definitionFound);
			defBuffer.append("_");
			
			definitions.add(i, defBuffer.toString());
		}
		found.setDefinition(definitions);
	}
	return found;
}


/**
 * 
 * @return Return a list of words
 */
public List<Word> findAllWord(){
	
	WordDao w = new WordDao();
	return w.findAllWords();
}

}

You can extract WordDao to class level as a field. Create set method.
After that in unit test you can mock WordDao and control what will be result of methods call. For the second method it something like:

WordDao wMocked = Mock(WordDao.class)
Word word1 = new...
Word word2 = new...
List<Word> words = List.of(word1, word2);
when(w.findAllWords()).thenReturn(words);
WordService ws = new WordService();
ws.setWordDao(wMocked);
Assert.equals(words, ws.findAllWords);