Learn French: Chaque don est utile pour aider notre association. - Each donation is useful to help our charity.

The word chaque means "each" or "every", and it is always used with a singular noun. So, both chaque and don must be singular. It also never changes spelling regardless of whether the noun is masculine or feminine.

Could I say tous les dons instead of chaque don here?

Yes, but it slightly changes the focus. Chaque don (each donation) highlights the individual contributions one by one. Tous les dons (all the donations) groups them together as a whole.

Why do we use pour before aider here?

In French, when you want to express "in order to do something", you use pour followed by the infinitive (unconjugated) form of the verb. Here, pour aider literally means "in order to help".

Does association just mean "association" here?

It can mean "association", but in everyday French, une association (short for une association caritative) is the most common way to say "a charity" or "a non-profit organization".

Is the word don related to the verb donner?