The single most distinctive feature of Ilokano grammar: the verb changes shape depending on which participant you want to highlight.
An English sentence like "The child will buy a mango" has one obvious subject: the child. Ilokano can instead put the mango itself in the subject position — and when it does, the verb's ending changes to match. This is the focus system, and it's the biggest structural difference from English grammar.
Active verb prefixes like ag-, -um-, and mang- put the doer of the action (the actor) in the subject position. The thing being acted on (the goal) is unmarked, introduced by ti/iti.
Gumátang ití manggá diáy ubíng.
The child will buy a mango.
actor (the child) is in focus; manggá 'mango' is the unfocused goal
Mangán ti manggá diáy ubíng.
The child will eat a mango.
mang- 'deliberative' active affix
Passive-style affixes like -en and -an instead put the thing being acted on in the subject position, marked with ti. The actor becomes a short possessive-style pronoun (na 'by him/her', ko 'by me') right after the verb.
Gatángen diáy ubíng diáy manggá.
The child will buy the mango.
-en marks goal focus; "the mango" (goal) is now the subject
Basáen na ta libró.
He will read that book.
na 'by him' is the actor; ta libró 'that book' is the focused goal
Ilokano can also focus the beneficiary (i-an), the instrument (pag-/pang-), or the reason/cause (i-, pag-an) of an action — each with its own verb affix. You don't need to memorize the whole system to get started; just recognize that a different verb ending usually means a different word has become the subject, not that the meaning changed completely.
Igatángan na ti manggá diáy balásang.
He will buy a mango for the lady.
i-an marks beneficiary focus — 'the lady' is now the subject
Pagpúted na ti kawáyan diáy bunéng ko.
He will use my big knife to cut bamboo.
pag- marks instrument focus — 'my knife' is now the subject
Grammar: Ch. 5, Verbal Sentences, from Constantino's Ilokano Reference Grammar (1971, CC BY-NC-SA 4.0).