1. By Synonym Sets: This is the most traditional method. Words with similar meanings are grouped together in sets called "synonym rings" or "synonym lists." The thesaurus then lists these sets alphabetically by the first word in each set. This makes it easy to find synonyms for a specific word by looking up the set it belongs to.
2. Alphabetically: Some thesauri list words alphabetically, just like a dictionary. This makes it easier to find a particular word quickly, but it doesn't offer the same grouping of synonyms that the first method provides. Within the alphabetical list, you might see synonym entries for each word.
These are just two main ways, and some thesauri might combine elements of both or use other organizational methods.