SCEA is Single Choice Early Action. This is non-binding. This is where you are allowed to only apply to one private university early. Examples include Stanford, Harvard, Yale, Princeton. You will find out in December if you are admitted, rejected, or deferred.
EA: This is just early action. You apply earlier and receive your decision earlier. It’s NON BINDING. meaning that you get the benefit of finding out early but you do not have to commit to attending if you get in. You can wait till May 1st. Your senior year will be less stressful if you get an early admit, and you will still be able to compare financial aid packages from your RD schools as well. You will find out in December if you are accepted, rejected, or deferred. UChicago, for example has EA.
ED: Early Decision. This is the BINDING option. You apply early,(Nov 1) get your decision early, (mid December) but if you are accepted you are legally bound to attend (unless there are extenuating financial circumstances). This is typically for your first choice and usually admit rates are a bit higher for the ED round. Of the Ivies, Cornell, Brown, Dartmouth, Columbia and UPenn have ED.
You need to check each schools’ rules regarding SCEA though. Some may allow you to apply to public univerities (like your state flagship) without breaking the rules.