Targeting
A lookalike audience tells Meta to find new people who resemble an existing group — for example, people similar to your past customers or past leads. It needs a source list of a reasonable size (Meta generally wants at least a few hundred contacts) to build a useful lookalike, which means it's not something a brand-new advertiser can use on day one.
Retargeting shows ads specifically to people who've already interacted with you somehow — visited your landing page without booking, or engaged with a past post — on the logic that a warm audience converts more easily than a cold one. This is powerful once you have enough traffic to retarget against, but with very low traffic, the audience is too small to be worth a dedicated campaign.
Both are genuinely useful tools for a business that has been running ads for a few months and has built up some data. For a brand-new campaign, focus on getting the fundamentals (offer, creative, basic geographic/age targeting) right first — these are the tools you graduate into, not start with.