You are right that 'would' can sound more formal than 'will' in requests. 'Would' is the more tentative and hypothetical version of 'will'. That is why 'Would you help me?' sounds more polite than 'Will you help me?'. 'Will' is often used for future time: J'aimerai = I will like/I'll like J'irai = I will go/I'll go Je le ferai = I will do it /I'll do it 'Would' is used for hypothetical situations: J'aimerais = I would like/I'd like J'irais = I would go/I'd go Je le ferais = I would do it/ I'd do it We use 'will' for probable situations in the future, for example: Si tu étudies, tu réussiras à l'examen = If you study, you will pass the exam. We use 'would' to imagine unreal and hypothetical situations : Si tu étudiais, tu réussirais à l'examen = If you studied, you would pass the exam.

"will" and "would" are common words which are used in different constructions and for various different reasons. Because of this, it makes most sense, in my opinion, to learn which word to use in specific contexts, and learn the form of the whole construction together. So I recommend that you find specific sentences where you don't understand the choice between "would" and "will" and we can perhaps help you more specifically.