The conditional tense is a tense used to express a hypothetical situation - in English, for example, we might say 'that would be a lot of fun'. It refers to something which may or may not happen in the future as opposed to something that has or definitely will take place. In order to form this tense - when regular - we must take the infinitive of the verb and add on the imperfect tense endings. These are as follows:
-ais
-ais
-ait
-ions
-iez
-aient
If the verb is regular - for example - 'parler' we simply add these endings to the end of the verb. E.g. 'je parlerais' = I would speak.
However, if the verb is irregular in the conditional tense, the infinitive stem must be learnt, e.g., 'être''s stem in the conditional tense is 'ser-' and vouloir becomes 'voudr-'.