’ll ; /l/ or /əl/, never with a full vowel ; is the informal contraction of will (sometimes shall), used after pronouns: I’ll call you tomorrow.
The apostrophe marks the missing letters of will and cannot be dropped: I’l is not a form.
I’ll help you with that. Here ’ll stands for will after the pronoun I. The word is often said quickly as /aɪl/, one syllable that sounds exactly like aisle, though in slower or more careful speech you may hear ’ll with a reduced vowel, /əl/, before the /l/.
We’ll see you at the station. In speech ’ll is just /l/ or /əl/ with no full vowel, so he’ll sounds like heel /hiːl/ with only /əl/ added at the end, and they’ll /ðeɪl/ keeps its full vowel and simply attaches the light /əl/. It attaches directly to pronouns like he, she and they in informal speech and writing, and the apostrophe is part of the spelling: it marks the missing letters of will, so he’ll cannot be written as he’l.
’ll normally attaches directly to a pronoun such as I, we, you, he, she, it or they, especially in informal English. In formal writing, many people prefer the full forms I will and we will, so choosing ’ll is a register choice, not just a spelling one. Related forms like there’ll also occur, but the pronoun-attached pattern is the well-established one, as in They’ll arrive by noon next to the more formal We will arrive by noon.
The spelling trap: the apostrophe sits exactly where wi was removed from will, so I’l is not a form. The correct spelling keeps it: I’ll.
They’ll arrive by noon. Informal, pronoun attached.
We will arrive by noon. Preferred in formal writing.