失敗を適切に処理するには、失敗の経験が役に立つ
what does に mean when it is placed after a sentence? can you give me a source so that I can learn this usage further
It's actually not “〜に” but “〜には”. This usage can never occur without “〜は”.
It's actually very similar in nuance to the infinitive in English, the sentence means:
Experience with failure is useful to properly deal with failure.
Other such sentences can be:
恋と呼ぶには気持ち悪い = It's disgusting to call this love.
ものを買うには金が必要だ = One needs money to buy things.
It's often said to indicate a purpose, but much as with English “to” that's not necessarily the case as one can see in the case of “恋と呼ぶには気持ち悪い”
Note that one can not use it like this:
パソコンを買うにはここに来た != I came here to buy a p.c..
For that sentence one must use:
パソコンを買いにここに来た
Attaching “〜に” to the continuative form of a verb. In general it's only used for abstract, general statements of purpose, not concrete instances.
https://jlptsensei.com/learn-japanese-grammar/%E3%81%AB%E3%81%AF-ni-wa-meaning/