"The purpose of this foundation is helping animals."
Translation:Cel tej fundacji to pomaganie zwierzętom.
Well... depends on how you construct the sentence.
You can write "Cel tej fundacji to pomaganie zwierzętom." or "Pomaganie zwierzętom to cel tej fundacji", the subject will technically be different, but both sentences will be correct.
But if you use the Instrumental construction, only one of those can take Instrumental.
Think about it like that: Helping animals can be "a purpose". You can put "a" here. But the purpose cannot be "a helping animals". This is why the only noun phrase that can be put in Instrumental is "The purpose". And while you're used to the Instrumental form being used on the 'right side' of the sentence, it can sometimes be on the left.
You may see Part 1,5 here: https://forum.duolingo.com/comment/16373167
there is some pattern though: verbs with the infinitive on -c of which the 1st singular ends in -kę (like tłuc, piec) have a verbal noun that ends in -czenie (tłuczenie, pieczenie). And verbs ending in -c of which the 1st singular stem ends in -gę often have a verbal noun ending in -żenie (strzyżenie, strzeżenie).
Obviously, móc and pomóc are an exception here.