The english equivalent is: would/should/could. The French use the conditionnel to soften-up commands. It is more polite.

To form: You leave the verb in its infinitive form (there are many exceptions) and add the imparfait endings,-ais, -ais. -ait, -ions.-iez,-aient, to each person. ex: Marie marche >> Marie marcher>> Marie marcherait.  Only with RE ending verbs do you drop the ‘e’ before adding the new endings. Ex: Tu descends>> tu descendre>> tu descendr>>> tu descendrais.