Learn French: Elles veulent un bon résultat, alors elles s'entraînent sérieusement. - They want a good result, so they train seriously.

It comes from the adjective for 'serious'. To form a regular adverb of manner in French (words that usually end in '-ly' in English), you take the feminine form of the adjective and add -ment. Here, the masculine adjective is sérieux, the feminine is sérieuse, and adding -ment gives us sérieusement.

Why is there an s' in front of entraînent?

Because the verb here is s'entraîner, which is a reflexive verb. It literally means 'to train oneself'. If you just said elles entraînent, it would mean they are training someone or something else (like a sports team). The s' (short for se) tells us they are the ones physically working out or practicing.

Why does bon come before the noun résultat instead of after it?

While most French adjectives go after the noun they describe, bon (good) is a common exception. You can remember this using the acronym BANGS (Beauty, Age, Number, Goodness, Size), which covers the main adjectives that go before the noun. Because bon describes 'Goodness', it comes right before résultat.

What is the dictionary form (infinitive) of veulent?

It comes from the irregular verb vouloir (to want). In the present tense, the ils/elles (they) form is veulent. It looks quite different from the infinitive, so it is one of those essential verbs you just have to memorize!